The C API code is distributed with MySQL. It is included in the
mysqlclient library and allows C programs to access a database.
Many of the clients in the MySQL source distribution are written in C. If you are looking for examples that demonstrate how to use the C API, take a look at these clients.
Most of the other client APIs (all except Java) use the mysqlclient
library to communicate with the MySQL server. This means that, for
example, you can take advantage of many of the same environment variables
that are used by other client programs, because they are referenced from the
library. See section 13.1 Overview of the different MySQL programs, for a list of these variables.
The client has a maximum communication buffer size. The size of the buffer that is allocated initially (16K bytes) is automatically increased up to the maximum size (the default maximum is 24M). Since buffer sizes are increased only as demand warrants, simply increasing the default maximum limit does not in inself cause more resources to be used. This size check is mostly a check for erroneous queries and communication packets.
The communication buffer must be large enough to contain a single SQL
statement (for client-to-server traffic) and one row of returned data (for
server-to-client traffic). Each thread's communication buffer is dynamically
enlarged to handle any query or row up to the maximum limit. For example, if
you have BLOB values that contain up to 16M of data, you must have a
communication buffer limit of at least 16M (in both server and client). The
client's default maximum is 24M, but the default maximum in the server is
1M. You can increase this by changing the value of the
max_allowed_packet parameter when the server is started. See section 11.2.3 Tuning server parameters.
The MySQL server shrinks each communication buffer to
net_buffer_length bytes after each query. For clients, the size of
the buffer associated with a connection is not decreased until the connection
is closed, at which time client memory is reclaimed.
If you are programming with threads, you should compile the
MySQL C API with --with-thread-safe-client. This will make
the C API thread safe per connection. You can let two threads share the same
connection as long as you do the following:
mysql_query() and mysql_store_result() no other thread is using
the same connection.
mysql_store_result().
mysql_use_result, you have to ensure that no other thread
is asking anything on the same connection until the result set is closed.
MYSQL
MYSQL_RES
SELECT, SHOW, DESCRIBE, EXPLAIN). The
information returned from a query is called the result set in the
remainder of this section.
MYSQL_ROW
mysql_fetch_row().
MYSQL_FIELD
MYSQL_FIELD structures for each field by
calling mysql_fetch_field() repeatedly. Field values are not part of
this structure; they are contained in a MYSQL_ROW structure.
MYSQL_FIELD_OFFSET
mysql_field_seek().) Offsets are field numbers
within a row, beginning at zero.
my_ulonglong
mysql_affected_rows(),
mysql_num_rows() and mysql_insert_id(). This type provides a
range of 0 to 1.84e19.
On some systems, attempting to print a value of type my_ulonglong
will not work. To print such a value, convert it to unsigned long
and use a %lu print format. Example:
printf (Number of rows: %lu\n", (unsigned long) mysql_num_rows(result));
The MYSQL_FIELD structure contains the members listed below:
char * name
char * table
table value is an empty string.
char * def
mysql_list_fields().
enum enum_field_types type
type value may be one of the following:
| Type value | Type meaning |
FIELD_TYPE_TINY | TINYINT field
|
FIELD_TYPE_SHORT | SMALLINT field
|
FIELD_TYPE_LONG | INTEGER field
|
FIELD_TYPE_INT24 | MEDIUMINT field
|
FIELD_TYPE_LONGLONG | BIGINT field
|
FIELD_TYPE_DECIMAL | DECIMAL or NUMERIC field
|
FIELD_TYPE_FLOAT | FLOAT field
|
FIELD_TYPE_DOUBLE | DOUBLE or REAL field
|
FIELD_TYPE_TIMESTAMP | TIMESTAMP field
|
FIELD_TYPE_DATE | DATE field
|
FIELD_TYPE_TIME | TIME field
|
FIELD_TYPE_DATETIME | DATETIME field
|
FIELD_TYPE_YEAR | YEAR field
|
FIELD_TYPE_STRING | String (CHAR or VARCHAR) field
|
FIELD_TYPE_BLOB | BLOB or TEXT field (use max_length to determine the maximum length)
|
FIELD_TYPE_SET | SET field
|
FIELD_TYPE_ENUM | ENUM field
|
FIELD_TYPE_NULL | NULL-type field
|
FIELD_TYPE_CHAR | Deprecated; use FIELD_TYPE_TINY instead
|
IS_NUM() macro to test whether or not a field has a
numeric type. Pass the type value to IS_NUM() and it
will evaluate to TRUE if the field is numeric:
if (IS_NUM(field->type))
printf("Field is numeric\n");
unsigned int length
unsigned int max_length
mysql_store_result() or mysql_list_fields(), this contains the
maximum length for the field. If you use mysql_use_result(), the
value of this variable is zero.
unsigned int flags
flags value may have zero
or more of the following bits set:
| Flag value | Flag meaning |
NOT_NULL_FLAG | Field can't be NULL
|
PRI_KEY_FLAG | Field is part of a primary key |
UNIQUE_KEY_FLAG | Field is part of a unique key |
MULTIPLE_KEY_FLAG | Field is part of a non-unique key. |
UNSIGNED_FLAG | Field has the UNSIGNED attribute
|
ZEROFILL_FLAG | Field has the ZEROFILL attribute
|
BINARY_FLAG | Field has the BINARY attribute
|
AUTO_INCREMENT_FLAG | Field has the AUTO_INCREMENT attribute
|
ENUM_FLAG | Field is an ENUM (deprecated)
|
BLOB_FLAG | Field is a BLOB or TEXT (deprecated)
|
TIMESTAMP_FLAG | Field is a TIMESTAMP (deprecated)
|
BLOB_FLAG, ENUM_FLAG and TIMESTAMP_FLAG flags
is deprecated because they indicate the type of a field rather than an
attribute of its type. It is preferable to test field->type against
FIELD_TYPE_BLOB, FIELD_TYPE_ENUM or FIELD_TYPE_TIMESTAMP
instead.
The example below illustrates a typical use of the flags value:
if (field->flags & NOT_NULL_FLAG)
printf("Field can't be null\n");
You may use the following convenience macros to determine the boolean
status of the flags value:
IS_NOT_NULL(flags) | True if this field is defined as NOT NULL
|
IS_PRI_KEY(flags) | True if this field is a primary key |
IS_BLOB(flags) | True if this field is a BLOB or TEXT (deprecated; test field->type instead)
|
unsigned int decimals
The functions available in the C API are listed below and are described in greater detail in the next section. See section 21.4 C API function descriptions.
| mysql_affected_rows() |
Returns the number of rows affected by the last UPDATE, DELETE or
INSERT query.
|
| mysql_close() | Closes a server connection. |
| mysql_connect() |
Connects to a MySQL server. This function is deprecated; use
mysql_real_connect() instead.
|
| mysql_change_user() | Change user and database on an open connection. |
| mysql_create_db() |
Creates a database. This function is deprecated; use the SQL command
CREATE DATABASE instead.
|
| mysql_data_seek() | Seeks to an arbitrary row in a query result set. |
| mysql_debug() |
Does a DBUG_PUSH with the given string.
|
| mysql_drop_db() |
Drops a database. This function is deprecated; use the SQL command
DROP DATABASE instead.
|
| mysql_dump_debug_info() | Makes the server write debug information to the log. |
| mysql_eof() |
Determines whether or not the last row of a result set has been read.
This function is deprecated; mysql_errno() or mysql_error()
may be used instead.
|
| mysql_errno() | Returns the error number for the most recently invoked MySQL function. |
| mysql_error() | Returns the error message for the most recently invoked MySQL function. |
| mysql_escape_string() | Escapes special characters in a string for use in a SQL statement. |
| mysql_fetch_field() | Returns the type of the next table field. |
| mysql_fetch_field_direct() | Returns the type of a table field, given a field number. |
| mysql_fetch_fields() | Returns an array of all field structures. |
| mysql_fetch_lengths() | Returns the lengths of all columns in the current row. |
| mysql_fetch_row() | Fetches the next row from the result set. |
| mysql_field_seek() | Puts the column cursor on a specified column. |
| mysql_field_count() | Returns the number of result columns for the most recent query. |
| mysql_field_tell() |
Returns the position of the field cursor used for the last
mysql_fetch_field().
|
| mysql_free_result() | Frees memory used by a result set. |
| mysql_get_client_info() | Returns client version information. |
| mysql_get_host_info() | Returns a string describing the connection. |
| mysql_get_proto_info() | Returns the protocol version used by the connection. |
| mysql_get_server_info() | Returns the server version number. |
| mysql_info() | Returns information about the most recently executed query. |
| mysql_init() |
Gets or initializes a MYSQL structure.
|
| mysql_insert_id() |
Returns the ID generated for an AUTO_INCREMENT column by the previous
query.
|
| mysql_kill() | Kill a given thread. |
| mysql_list_dbs() | Returns database names matching a simple regular expression. |
| mysql_list_fields() | Returns field names matching a simple regular expression. |
| mysql_list_processes() | Returns a list of the current server threads. |
| mysql_list_tables() | Returns table names matching a simple regular expression. |
| mysql_num_fields() | Returns the number of columns in a result set. |
| mysql_num_rows() | Returns the number of rows in a result set. |
| mysql_options() |
Set connect options for mysql_connect().
|
| mysql_ping() | Checks whether or not the connection to the server is working, reconnecting as necessary. |
| mysql_query() | Executes a SQL query specified as a null-terminated string. |
| mysql_real_connect() | Connects to a MySQL server. |
| mysql_real_query() | Executes a SQL query specified as a counted string. |
| mysql_reload() | Tells the server to reload the grant tables. |
| mysql_row_seek() |
Seeks to a row in a result set, using value returned from
mysql_row_tell().
|
| mysql_row_tell() | Returns the row cursor position. |
| mysql_select_db() | Connects to a database. |
| mysql_shutdown() | Shuts down the database server. |
| mysql_stat() | Returns the server status as a string. |
| mysql_store_result() | Retrieves a complete result set to the client. |
| mysql_thread_id() | Returns the current thread ID. |
| mysql_use_result() | Initiates a row-by-row result set retrieval. |
To connect to the server, call mysql_init() to initialize a connection
handler, then call mysql_real_connect() with that handler (along with
other information such as the hostname, user name and password). When you
are done with the connection, call mysql_close() to terminate it.
While a connection is active, the client may send SQL queries to the server
using mysql_query() or mysql_real_query(). The difference
between the two is that mysql_query() expects the query to be
specified as a null-terminated string whereas mysql_real_query()
expects a counted string. If the string contains binary data (which may
include null bytes), you must use mysql_real_query().
For each non-SELECT query (e.g., INSERT, UPDATE,
DELETE), you can found out how many rows were affected (changed)
by calling mysql_affected_rows().
For SELECT queries, you retrieve the selected rows as a result set.
(Note that some statements are SELECT-like in that they return rows.
These include SHOW, DESCRIBE and EXPLAIN. They should
be treated the same way as SELECT statements.)
There are two ways for a client to process result sets. One way is to
retrieve the entire result set all at once by calling
mysql_store_result(). This function acquires from the server all the
rows returned by the query and stores them in the client. The second way is
for the client to initiate a row-by-row result set retrieval by calling
mysql_use_result(). This function initializes the retrieval, but does
not actually get any rows from the server.
In both cases, you access rows by calling mysql_fetch_row(). With
mysql_store_result(), mysql_fetch_row() accesses rows that have
already been fetched from the server. With mysql_use_result(),
mysql_fetch_row() actually retrieves the row from the server.
Information about as the size of the data values in each row is available by
calling mysql_fetch_lengths().
After you are done with a result set, call mysql_free_result()
to free the memory used for it.
The two retrieval mechanisms are complementary. Client programs should
choose the approach that is most appropriate for their requirements.
In practice, clients tend to use mysql_store_result() more
commonly.
An advantage of mysql_store_result() is that since the rows have all
been fetched to the client, you not only can access rows sequentially, you
can move back and forth in the result set using mysql_data_seek() or
mysql_row_seek() to change the current row position within the result
set. You can also find out how many rows there are by calling
mysql_num_rows(). On the other hand, the memory requirements for
mysql_store_result() may be very high for large result sets and you
are more likely to encounter out-of-memory conditions.
An advantage of mysql_use_result() is that the client requires less
memory for the result set since it maintains only one row at a time (and
since there is less allocation overhead, mysql_use_result() can be
faster). Disadvantages are that you must process each row quickly to avoid
tying up the server, you don't have random access to rows within the result
set (you can only access rows sequentially), and you don't know how many rows
are in the result set until you have retrieved them all. Furthermore, you
must retrieve all the rows even if you determine in mid-retrieval that
you've found the information you were looking for.
The API makes it possible for clients to respond appropriately to
queries (retrieving rows only as necessary) without knowing whether or
not the query is a SELECT. You can do this by calling
mysql_store_result() after each mysql_query() (or
mysql_real_query()). If the result set call succeeds, the query
was a SELECT and you can read the rows. If the result set call
fails, call mysql_field_count() to determine whether or not a
result was actually to be expected. If mysql_field_count()
returns zero, the query returned no data (indicating that it was an
INSERT, UPDATE, DELETE, etc.), and thus not
expected to return rows. If mysql_field_count() is non-zero, the
query should have returned rows, but didn't. This indicates that the
query was a SELECT that failed. See the description for
mysql_field_count() for an example of how this can be done.
Both mysql_store_result() and mysql_use_result() allow you to
obtain information about the fields that make up the result set (the number
of fields, their names and types, etc.). You can access field information
sequentially within the row by calling mysql_fetch_field() repeatedly,
or by field number within the row by calling
mysql_fetch_field_direct(). The current field cursor position may be
changed by calling mysql_field_seek(). Setting the field cursor
affects subsequent calls to mysql_fetch_field(). You can also get
information for fields all at once by calling mysql_fetch_fields().
For detecting and reporting errors, MySQL provides access to error
information by means of the mysql_errno() and mysql_error()
functions. These return the error code or error message for the most
recently invoked function that can succeed or fail, allowing you to determine
when an error occurred and what it was.
In the descriptions below, a parameter or return value of NULL means
NULL in the sense of the C programming language, not a
MySQL NULL value.
Functions that return a value generally return a pointer or an integer.
Unless specified otherwise, functions returning a pointer return a
non-NULL value to indicate success or a NULL value to indicate
an error, and functions returning an integer return zero to indicate success
or non-zero to indicate an error. Note that ``non-zero'' means just that.
Unless the function description says otherwise, do not test against a value
other than zero:
if (result) /* correct */
... error ...
if (result < 0) /* incorrect */
... error ...
if (result == -1) /* incorrect */
... error ...
When a function returns an error, the Errors subsection of the
function description lists the possible types of errors. You can
find out which of these occurred by calling mysql_errno().
A string representation of the error may be obtained by calling
mysql_error().
mysql_affected_rows()
my_ulonglong mysql_affected_rows(MYSQL *mysql)
Returns the number of rows affected (changed) by the last UPDATE,
DELETE or INSERT query. May be called immediately after
mysql_query() for UPDATE, DELETE or INSERT
statements. For SELECT statements, mysql_affected_rows()
works like mysql_num_rows().
mysql_affected_rows() is currently implemented as a macro.
An integer greater than zero indicates the number of rows affected or
retrieved. Zero indicates that no records matched the WHERE clause in
the query or that no query has yet been executed. -1 indicates that the
query returned an error or that, for a SELECT query,
mysql_affected_rows() was called prior to calling
mysql_store_result().
None.
mysql_query(&mysql,"UPDATE products SET cost=cost*1.25 WHERE group=10");
printf("%d products updated",mysql_affected_rows(&mysql));
mysql_close()
void mysql_close(MYSQL *mysql)
Closes a previously opened connection. mysql_close() also deallocates
the connection handle pointed to by mysql if the handle was allocated
automatically by mysql_init() or mysql_connect().
None.
CR_COMMANDS_OUT_OF_SYNC
CR_SERVER_GONE_ERROR
CR_SERVER_LOST
CR_UNKNOWN_ERROR
mysql_connect()
MYSQL *mysql_connect(MYSQL *mysql, const char *host, const char *user, const char *passwd)
This function is deprecated. It is preferable to use
mysql_real_connect() instead.
mysql_connect() attempts to establish a connection to a MySQL
database engine running on host. mysql_connect() must complete
successfully before you can execute any of the other API functions, with the
exception of mysql_get_client_info().
The meanings of the parameters are the same as for the corresponding
parameters for mysql_real_connect() with the difference that the
connection paramater may be NULL. In this case the C API
allocates memory for the connection structure automatically and frees it
when you call mysql_close(). The disadvantage of this approach is
that you can't retrieve an error message if the connection fails. (To
get error information from mysql_errno() or mysql_error(),
you must provide a valid MYSQL pointer.)
Same as for mysql_real_connect().
Same as for mysql_real_connect().
mysql_change_user()
my_bool mysql_change_user(MYSQL *mysql, const char *user, const
char *password, const char *db)
Changes the user and causes the database specified by db to
become the default (current) database on the connection specified by
mysql. In subsequent queries, this database is the default for
table references that do not include an explicit database specifier.
This function was introduced in MySQL 3.23.3.
mysql_change_user() fails unless the connected user can be
authenticated or if he doesn't have permission to use the database. In
this case the user and database are not changed
The db parameter may be set to NULL if you don't want to have a
default database.
Zero for success. Non-zero if an error occurred.
The same that you can get from mysql_real_connect().
CR_COMMANDS_OUT_OF_SYNC
CR_SERVER_GONE_ERROR
CR_SERVER_LOST
CR_UNKNOWN_ERROR
ER_UNKNOWN_COM_ERROR
ER_ACCESS_DENIED_ERROR
ER_BAD_DB_ERROR
ER_DBACCESS_DENIED_ERROR
ER_WRONG_DB_NAME
if (mysql_change_user(&mysql, "user", "password", "new_database"))
{
fprintf(stderr, "Failed to change user. Error: %s\n",
mysql_error(&mysql));
}
mysql_create_db()
int mysql_create_db(MYSQL *mysql, const char *db)
Creates the database named by the db parameter.
This function is deprecated. It is preferable to use mysql_query()
to issue a SQL CREATE DATABASE statement instead.
Zero if the database was created successfully. Non-zero if an error occurred.
CR_COMMANDS_OUT_OF_SYNC
CR_SERVER_GONE_ERROR
CR_SERVER_LOST
CR_UNKNOWN_ERROR
if(mysql_create_db(&mysql, "my_database"))
{
fprintf(stderr, "Failed to create new database. Error: %s\n",
mysql_error(&mysql));
}
mysql_data_seek()
void mysql_data_seek(MYSQL_RES *result, unsigned long long offset)
Seeks to an arbitrary row in a query result set. This requires that the
result set structure contains the entire result of the query, so
mysql_data_seek() may be used in conjunction only with
mysql_store_result(), not with mysql_use_result().
The offset should be a value in the range from 0 to
mysql_num_rows(result)-1.
None.
None.
mysql_debug()
void mysql_debug(char *debug)
Does a DBUG_PUSH with the given string. mysql_debug() uses the
Fred Fish debug library. To use this function, you must compile the client
library to support debugging.
See section G.1 Debugging a MySQL server. See section G.2 Debugging a MySQL client.
None.
None.
The call shown below causes the client library to generate a trace file in `/tmp/client.trace' on the client machine:
mysql_debug("d:t:O,/tmp/client.trace");
mysql_drop_db()
int mysql_drop_db(MYSQL *mysql, const char *db)
Drops the database named by the db parameter.
This function is deprecated. It is preferable to use mysql_query()
to issue a SQL DROP DATABASE statement instead.
Zero if the database was dropped successfully. Non-zero if an error occurred.
CR_COMMANDS_OUT_OF_SYNC
CR_SERVER_GONE_ERROR
CR_SERVER_LOST
CR_UNKNOWN_ERROR
if(mysql_drop_db(&mysql, "my_database"))
fprintf(stderr, "Failed to drop the database: Error: %s\n",
mysql_error(&mysql));
mysql_dump_debug_info()
int mysql_dump_debug_info(MYSQL *mysql)
Instructs the server to write some debug information to the log. The connected user must have the process privilege for this to work.
Zero if the command was successful. Non-zero if an error occurred.
CR_COMMANDS_OUT_OF_SYNC
CR_SERVER_GONE_ERROR
CR_SERVER_LOST
CR_UNKNOWN_ERROR
mysql_eof()
my_bool mysql_eof(MYSQL_RES *result)
This function is deprecated. mysql_errno() or mysql_error()
may be used instead.
mysql_eof() determines whether or not the last row of a result
set has been read.
If you acquire a result set from a successful call to
mysql_store_result(), the client receives the entire set in one
operation. In this case, a NULL return from mysql_fetch_row()
always means the end of the result set has been reached and it is
unnecessary to call mysql_eof().
On the other hand, if you use mysql_use_result() to initiate a result
set retrieval, the rows of the set are obtained from the server one by one as
you call mysql_fetch_row() repeatedly. Because an error may occur on
the connection during this process, a NULL return value from
mysql_fetch_row() does not necessarily mean the end of the result set
was reached normally. In this case, you can use mysql_eof() to
determine what happened. mysql_eof() returns a non-zero value if the
end of the result set was reached and zero if an error occurred.
Historically, mysql_eof() predates the standard MySQL error
functions mysql_errno() and mysql_error(). Since those error
functions provide the same information, their use is preferred over
mysql_eof(), which is now deprecated. (In fact, they provide more
information, since mysql_eof() returns only a boolean value whereas
the error functions indicate a reason for the error when one occurs.)
Zero if an error occurred. Non-zero if the end of the result set has been reached.
None.
The following example shows how you might use mysql_eof():
mysql_query(&mysql,"SELECT * FROM some_table");
result = mysql_use_result(&mysql);
while((row = mysql_fetch_row(result)))
{
// do something with data
}
if(!mysql_eof(result)) // mysql_fetch_row() failed due to an error
{
fprintf(stderr, "Error: %s\n", mysql_error(&mysql));
}
However, you can achieve the same effect with the standard MySQL error functions:
mysql_query(&mysql,"SELECT * FROM some_table");
result = mysql_use_result(&mysql);
while((row = mysql_fetch_row(result)))
{
// do something with data
}
if(mysql_errno(&mysql)) // mysql_fetch_row() failed due to an error
{
fprintf(stderr, "Error: %s\n", mysql_error(&mysql));
}
mysql_errno()
unsigned int mysql_errno(MYSQL *mysql)
For the connection specified by mysql, mysql_errno() returns
the error code for the most recently invoked API function that can succeed
or fail. A return value of zero means that no error occurred. Client error
message numbers are listed in the MySQL `errmsg.h' header file.
Server error message numbers are listed in `mysqld_error.h'
An error code value. Zero if no error occurred.
None.
mysql_error()
char *mysql_error(MYSQL *mysql)
For the connection specified by mysql, mysql_error() returns
the error message for the most recently invoked API function that can succeed
or fail. An empty string ("") is returned if no error occurred.
This means the following two tests are equivalent:
if(mysql_errno(&mysql))
{
// an error occurred
}
if(mysql_error(&mysql)[0] != '\0')
{
// an error occurred
}
The language of the client error messages may be changed by recompiling the MySQL client library. Currently you can choose error messages in several different languages. See section 10.1 What languages are supported by MySQL?.
A character string that describes the error. An empty string if no error occurred.
None.
mysql_escape_string()
unsigned int mysql_escape_string(char *to, const char *from, unsigned int length)
Encodes the string in from to an escaped SQL string that can be sent
to the server in a SQL statement, places the result in to, and adds a
terminating null byte. Characters encoded are NUL (ASCII 0),
`\n', `\r', `\', `'', `"' and Control-Z
(see section 7.1 Literals: how to write strings and numbers).
The string pointed to by from must be length bytes long. You
must allocate the to buffer to be at least length*2+1 bytes
long. (In the worse case, each character may need to be encoded as using two
bytes, and you need room for the terminating null byte.) When
mysql_escape_string() returns, the contents of to will be a
null-terminated string. The return value is the length of the encoded
string, not including the terminating null character.
char query[1000],*end;
end = strmov(query,"INSERT INTO test_table values(");
*end++ = '\'';
end += mysql_escape_string(end,"What's this",11);
*end++ = '\'';
*end++ = ',';
*end++ = '\'';
end += mysql_escape_string(end,"binary data: \0\r\n",16);
*end++ = '\'';
*end++ = ')';
if (mysql_real_query(&mysql,query,(unsigned int) (end - query)))
{
fprintf(stderr, "Failed to insert row, Error: %s\n",
mysql_error(&mysql));
}
The strmov() function used in the example is included in the
mysqlclient library and works like strcpy() but returns a
pointer to the terminating null of the first parameter.
The length of the value placed into to, not including the
terminating null character.
None.
mysql_fetch_field()
MYSQL_FIELD *mysql_fetch_field(MYSQL_RES *result)
Returns the definition of one column of a result set as a MYSQL_FIELD
structure. Call this function repeatedly to retrieve information about all
columns in the result set. mysql_fetch_field() returns NULL
when no more fields are left.
mysql_fetch_field() is reset to return information about the first
field each time you execute a new SELECT query. The field returned by
mysql_fetch_field() is also affected by calls to
mysql_field_seek().
If you've called mysql_query() to perform a SELECT on a table
but have not called mysql_store_result(), MySQL returns the
default blob length (8K bytes) if you call mysql_fetch_field() to ask
for the length of a BLOB field. (The 8K size is chosen because
MySQL doesn't know the maximum length for the BLOB. This
should be made configurable sometime.) Once you've retrieved the result set,
field->max_length contains the length of the largest value for this
column in the specific query.
The MYSQL_FIELD structure for the current column. NULL
if no columns are left.
None.
MYSQL_FIELD *field;
while((field = mysql_fetch_field(result)))
{
printf("field name %s\n", field->name);
}
mysql_fetch_fields()
MYSQL_FIELD *mysql_fetch_fields(MYSQL_RES *result)
Returns an array of all MYSQL_FIELD structures for a result set.
Each structure provides the field definition for one column of the result
set.
An array of MYSQL_FIELD structures for all columns of a result set.
None.
unsigned int num_fields;
unsigned int i;
MYSQL_FIELD *fields;
num_fields = mysql_num_fields(result);
fields = mysql_fetch_fields(result);
for(i = 0; i < num_fields; i++)
{
printf("Field %u is %s\n", i, fields[i].name);
}
mysql_fetch_field_direct()
MYSQL_FIELD *mysql_fetch_field_direct(MYSQL_RES *result, unsigned int fieldnr)
Given a field number fieldnr for a column within a result set, returns
that column's field definition as a MYSQL_FIELD structure. You may use
this function to retrieve the definition for an arbitrary column. The value
of fieldnr should be in the range from 0 to
mysql_num_fields(result)-1.
The MYSQL_FIELD structure for the specified column.
None.
unsigned int num_fields;
unsigned int i;
MYSQL_FIELD *field;
num_fields = mysql_num_fields(result);
for(i = 0; i < num_fields; i++)
{
field = mysql_fetch_field_direct(result, i);
printf("Field %u is %s\n", i, field->name);
}
mysql_fetch_lengths()
unsigned long *mysql_fetch_lengths(MYSQL_RES *result)
Returns the lengths of the columns of the current row within a result set.
If you plan to copy field values, this length information is also useful for
optimization, because you can avoid calling strlen(). In addition, if
the result set contains binary data, you must use this function to
determine the size of the data, because strlen() returns incorrect
results for any field containing null characters.
The length for empty columns and for columns containing NULL values is
zero. To see how to distinguish these two cases, see the description for
mysql_fetch_row().
An array of unsigned long integers representing the size of each column (not
including any terminating null characters).
NULL if an error occurred.
mysql_fetch_lengths() is valid only for the current row of the result
set. It returns NULL if you call it before calling
mysql_fetch_row() or after retrieving all rows in the result.
MYSQL_ROW row;
unsigned long *lengths;
unsigned int num_fields;
unsigned int i;
row = mysql_fetch_row(result);
if (row)
{
num_fields = mysql_num_fields(result);
lengths = mysql_fetch_lengths(result);
for(i = 0; i < num_fields; i++)
{
printf("Column %u is %lu bytes in length.\n", i, lengths[i]);
}
}
mysql_fetch_row()
MYSQL_ROW mysql_fetch_row(MYSQL_RES *result)
Retrieves the next row of a result set. When used after
mysql_store_result(), mysql_fetch_row() returns NULL
when there are no more rows to retrieve. When used after
mysql_use_result(), mysql_fetch_row() returns NULL when
there are no more rows to retrieve or if an error occurred.
The number of values in the row is given by mysql_num_fields(result).
If row holds the return value from a call to mysql_fetch_row(),
pointers to the values are accessed as row[0] to
row[mysql_num_fields(result)-1]. NULL values in the row are
indicated by NULL pointers.
The lengths of the field values in the row may be obtained by calling
mysql_fetch_lengths(). Empty fields and fields containing
NULL both have length 0; you can distinguish these by checking
the pointer for the field value. If the pointer is NULL, the field
is NULL; otherwise the field is empty.
A MYSQL_ROW structure for the next row. NULL if
there are no more rows to retrieve or if an error occurred.
CR_SERVER_LOST
CR_UNKNOWN_ERROR
MYSQL_ROW row;
unsigned int num_fields;
unsigned int i;
num_fields = mysql_num_fields(result);
while ((row = mysql_fetch_row(result)))
{
unsigned long *lengths;
lengths = mysql_fetch_lengths(result);
for(i = 0; i < num_fields; i++)
{
printf("[%.*s] ", (int) lengths[i], row[i] ? row[i] : "NULL");
}
printf("\n");
}
mysql_field_count()
unsigned int mysql_field_count(MYSQL *mysql)
If you are using a version of MySQL earlier than 3.22.24, you
should use unsigned int mysql_num_fields(MYSQL *mysql) instead.
Returns the number of columns for the most recent query on the connection.
The normal use of this function is when mysql_store_result()
returned NULL (and thus you have no result set pointer).
In this case, you can call mysql_field_count() to
determine whether or not mysql_store_result() should have produced a
non-empty result. This allows the client program to take proper action
without knowing whether or not the query was a SELECT (or
SELECT-like) statement. The example shown below illustrates how this
may be done.
See section 21.4.51 Why is it that after mysql_query() returns success, mysql_store_result() sometimes returns NULL?.
An unsigned integer representing the number of fields in a result set.
None.
MYSQL_RES *result;
unsigned int num_fields;
unsigned int num_rows;
if (mysql_query(&mysql,query_string))
{
// error
}
else // query succeeded, process any data returned by it
{
result = mysql_store_result(&mysql);
if (result) // there are rows
{
num_fields = mysql_num_fields(result);
// retrieve rows, then call mysql_free_result(result)
}
else // mysql_store_result() returned nothing; should it have?
{
if(mysql_field_count(&mysql) == 0)
{
// query does not return data
// (it was not a SELECT)
num_rows = mysql_affected_rows(&mysql);
}
else // mysql_store_result() should have returned data
{
fprintf(stderr, "Error: %s\n", mysql_error(&mysql));
}
}
}
An alternative is to replace the mysql_field_count(&mysql) call with
mysql_errno(&mysql). In this case, you are checking directly for an
error from mysql_store_result() rather than inferring from the value
of mysql_field_count() whether or not the statement was a
SELECT.
mysql_field_seek()
MYSQL_FIELD_OFFSET mysql_field_seek(MYSQL_RES *result, MYSQL_FIELD_OFFSET offset)
Sets the field cursor to the given offset. The next call to
mysql_fetch_field() will retrieve the field definition of the column
associated with that offset.
To seek to the beginning of a row, pass an offset value of zero.
The previous value of the field cursor.
None.
mysql_field_tell()
MYSQL_FIELD_OFFSET mysql_field_tell(MYSQL_RES *result)
Returns the position of the field cursor used for the last
mysql_fetch_field(). This value can be used as an argument to
mysql_field_seek().
The current offset of the field cursor.
None.
mysql_free_result()
void mysql_free_result(MYSQL_RES *result)
Frees the memory allocated for a result set by mysql_store_result(),
mysql_use_result(), mysql_list_dbs(), etc. When you are done
with a result set, you must free the memory it uses by calling
mysql_free_result().
None.
None.
mysql_get_client_info()
char *mysql_get_client_info(void)
Returns a string that represents the client library version.
A character string that represents the MySQL client library version.
None.
mysql_get_host_info()
char *mysql_get_host_info(MYSQL *mysql)
Returns a string describing the type of connection in use, including the server host name.
A character string representing the server host name and the connection type.
None.
mysql_get_proto_info()
unsigned int mysql_get_proto_info(MYSQL *mysql)
Returns the protocol version used by current connection.
An unsigned integer representing the protocol version used by the current connection.
None.
mysql_get_server_info()
char *mysql_get_server_info(MYSQL *mysql)
Returns a string that represents the server version number.
A character string that represents the server version number.
None.
mysql_info()
char *mysql_info(MYSQL *mysql)
Retrieves a string providing information about the most recently executed
query, but only for the statements listed below. For other statements,
mysql_info() returns NULL. The format of the string varies
depending on the type of query, as described below. The numbers are
illustrative only; the string will contain values appropriate for the query.
INSERT INTO ... SELECT ...
Records: 100 Duplicates: 0 Warnings: 0
INSERT INTO ... VALUES (...),(...),(...)...
Records: 3 Duplicates: 0 Warnings: 0
LOAD DATA INFILE ...
Records: 1 Deleted: 0 Skipped: 0 Warnings: 0
ALTER TABLE
Records: 3 Duplicates: 0 Warnings: 0
UPDATE
Rows matched: 40 Changed: 40 Warnings: 0
Note that mysql_info() returns a non-NULL value for the
INSERT ... VALUES statement only if multiple value lists are
specified in the statement.
A character string representing additional information about the most
recently executed query. NULL if no information is available for the
query.
None.
mysql_init()
MYSQL *mysql_init(MYSQL *mysql)
Allocates or initializes a MYSQL object suitable for
mysql_real_connect(). If mysql is a NULL pointer, the
function allocates, initializes and returns a new object. Otherwise the
object is initialized and the address of the object is returned. If
mysql_init() allocates a new object, it will be freed when
mysql_close() is called to close the connection.
An initialized MYSQL* handle. NULL if there was
insufficient memory to allocate a new object.
In case of insufficient memory, NULL is returned.
mysql_insert_id()
my_ulonglong mysql_insert_id(MYSQL *mysql)
Returns the ID generated for an AUTO_INCREMENT column by the previous
query. Use this function after you have performed an INSERT query
into a table that contains an AUTO_INCREMENT field.
Note that mysql_insert_id() returns 0 if the previous query
does not generate an AUTO_INCREMENT value. If you need to save
the value for later, be sure to call mysql_insert_id() immediately
after the query that generates the value.
Also note that the value of the SQL LAST_INSERT_ID() function always
contains the most recently generated AUTO_INCREMENT value, and is
not reset between queries since the value of that function is maintained
in the server.
The value of the AUTO_INCREMENT field that was updated by the previous
query. Returns zero if there was no previous query on the connection or if
the query did not update an AUTO_INCREMENT value.
None.
mysql_kill()
int mysql_kill(MYSQL *mysql, unsigned long pid)
Asks the server to kill the thread specified by pid.
Zero for success. Non-zero if an error occurred.
CR_COMMANDS_OUT_OF_SYNC
CR_SERVER_GONE_ERROR
CR_SERVER_LOST
CR_UNKNOWN_ERROR
mysql_list_dbs()
MYSQL_RES *mysql_list_dbs(MYSQL *mysql, const char *wild)
Returns a result set consisting of database names on the server that match
the simple regular expression specified by the wild parameter.
wild may contain the wildcard characters `%' or `_', or may
be a NULL pointer to match all databases. Calling
mysql_list_dbs() is similar to executing the query SHOW
databases [LIKE wild].
You must free the result set with mysql_free_result().
A MYSQL_RES result set for success. NULL if an error occurred.
CR_COMMANDS_OUT_OF_SYNC
CR_OUT_OF_MEMORY
CR_SERVER_GONE_ERROR
CR_SERVER_LOST
CR_UNKNOWN_ERROR
mysql_list_fields()
MYSQL_RES *mysql_list_fields(MYSQL *mysql, const char *table, const char *wild)
Returns a result set consisting of field names in the given table that match
the simple regular expression specified by the wild parameter.
wild may contain the wildcard characters `%' or `_', or may
be a NULL pointer to match all fields. Calling
mysql_list_fields() is similar to executing the query SHOW
COLUMNS FROM tbl_name [LIKE wild].
Note that it's recommended that you use SHOW COLUMNS FROM tbl_name
instead of mysql_list_fields().
You must free the result set with mysql_free_result().
A MYSQL_RES result set for success. NULL if an error occurred.
CR_COMMANDS_OUT_OF_SYNC
CR_SERVER_GONE_ERROR
CR_SERVER_LOST
CR_UNKNOWN_ERROR
mysql_list_processes()
MYSQL_RES *mysql_list_processes(MYSQL *mysql)
Returns a result set describing the current server threads. This is the same
kind of information as that reported by mysqladmin processlist or
a SHOW PROCESSLIST query.
You must free the result set with mysql_free_result().
A MYSQL_RES rsult set for success. NULL if an error occurred.
CR_COMMANDS_OUT_OF_SYNC
CR_SERVER_GONE_ERROR
CR_SERVER_LOST
CR_UNKNOWN_ERROR
mysql_list_tables()
MYSQL_RES *mysql_list_tables(MYSQL *mysql, const char *wild)
Returns a result set consisting of table names in the current database that
match the simple regular expression specified by the wild parameter.
wild may contain the wildcard characters `%' or `_', or may
be a NULL pointer to match all tables. Calling
mysql_list_tables() is similar to executing the query SHOW
tables [LIKE wild].
You must free the result set with mysql_free_result().
A MYSQL_RES result set for success. NULL if an error occurred.
CR_COMMANDS_OUT_OF_SYNC
CR_SERVER_GONE_ERROR
CR_SERVER_LOST
CR_UNKNOWN_ERROR
mysql_num_fields()
unsigned int mysql_num_fields(MYSQL_RES *result)
or
unsigned int mysql_num_fields(MYSQL *mysql)
The second form doesn't work on MySQL 3.22.24 or newer. To pass a
MYSQL* argument, you must use
unsigned int mysql_field_count(MYSQL *mysql) instead.
Returns the number of columns in a result set.
Note that you can get the number of columns either from a pointer to a result
set or to a connection handle. You would use the connection handle if
mysql_store_result() or mysql_user_result() returned
NULL (and thus you have no result set pointer). In this case, you can
call mysql_field_count() to determine whether or not
mysql_store_result() should have produced a non-empty result. This
allows the client program to take proper action without knowing whether or
not the query was a SELECT (or SELECT-like) statement. The
example shown below illustrates how this may be done.
See section 21.4.51 Why is it that after mysql_query() returns success, mysql_store_result() sometimes returns NULL?.
An unsigned integer representing the number of fields in a result set.
None.
MYSQL_RES *result;
unsigned int num_fields;
unsigned int num_rows;
if (mysql_query(&mysql,query_string))
{
// error
}
else // query succeeded, process any data returned by it
{
result = mysql_store_result(&mysql);
if (result) // there are rows
{
num_fields = mysql_num_fields(result);
// retrieve rows, then call mysql_free_result(result)
}
else // mysql_store_result() returned nothing; should it have?
{
if (mysql_errno(&mysql))
{
fprintf(stderr, "Error: %s\n", mysql_error(&mysql));
}
else if (mysql_field_count(&mysql) == 0)
{
// query does not return data
// (it was not a SELECT)
num_rows = mysql_affected_rows(&mysql);
}
}
}
An alternative (if you KNOW that your query should have returned a result set)
is to replace the mysql_errno(&mysql) call with a check if
mysql_field_count(&mysql) is = 0. This will only happen if something
went wrong.
mysql_num_rows()
my_ulonglong mysql_num_rows(MYSQL_RES *result)
Returns the number of rows in the result set.
The use of mysql_num_rows() depends on whether you use
mysql_store_result() or mysql_use_result() to return the result
set. If you use mysql_store_result(), mysql_num_rows() may be
called immediately. If you use mysql_use_result(),
mysql_num_rows() will not return the correct value until all the rows
in the result set have been retrieved.
The number of rows in the result set.
None.
mysql_options()
int mysql_options(MYSQL *mysql, enum mysql_option option, const char *arg)
Can be used to set extra connect options and affect behavior for a connection. This function may be called multiple times to set several options.
mysql_options() should be called after mysql_init() and before
mysql_connect() or mysql_real_connect().
The option argument is the option that you want to set; the arg
argument is the value for the option. If the option is an integer, then
arg should point to the value of the integer.
Possible options values:
| Option | Argument type | Function |
MYSQL_OPT_CONNECT_TIMEOUT | unsigned int * | Connect timeout in seconds. |
MYSQL_OPT_COMPRESS | Not used | Use the compressed client/server protocol. |
MYSQL_OPT_NAMED_PIPE | Not used | Use named pipes to connect to a MySQL server on NT. |
MYSQL_INIT_COMMAND | char * | Command to execute when connecting to the MySQL server. Will automatically be re-executed when reconnecting. |
MYSQL_READ_DEFAULT_FILE | char * | Read options from the named option file instead of from `my.cnf'. |
MYSQL_READ_DEFAULT_GROUP | char * | Read options from the named group from `my.cnf' or the file specified with MYSQL_READ_DEFAULT_FILE.
|
Note that the group client is always read if you use
MYSQL_READ_DEFAULT_FILE or MYSQL_READ_DEFAULT_GROUP.
The specified group in the option file may contain the following options:
compress | Use the compressed client/server protocol. |
database | Connect to this database if there no database was specified in the connect command |
debug | Debug options |
host | Default host name |
init-command | Command to execute when connecting to MySQL server. Will automatically be re-executed when reconnecting. |
password | Default password |
pipe | Use named pipes to connect to a MySQL server on NT. |
port | Default port number |
return-found-rows | Tell mysql_info() to return found rows instead of updated rows when using UPDATE.
|
socket | Default socket number |
timeout | Connect timeout in seconds. |
user | Default user |
For more information about option files, see section 4.15.4 Option files.
Zero for success. Non-zero if you used an unknown option.
MYSQL mysql;
mysql_init(&mysql);
mysql_options(&mysql,MYSQL_OPT_COMPRESS,0);
mysql_options(&mysql,MYSQL_READ_DEFAULT_GROUP,"odbc");
if (!mysql_real_connect(&mysql,"host","user","passwd","database",0,NULL,0))
{
fprintf(stderr, "Failed to connect to database: Error: %s\n",
mysql_error(&mysql));
}
The above requests the client to use the compressed client/server protocol and
read the additional options from the odbc section in the my.cnf
file.
mysql_ping()
int mysql_ping(MYSQL *mysql)
Checks whether or not the connection to the server is working. If it has gone down, an automatic reconnection is attempted.
This function can be used by clients that remain idle for a long while, to check whether or not the server has closed the connection and reconnect if necessary.
Zero if the server is alive. Non-zero if an error occurred.
CR_COMMANDS_OUT_OF_SYNC
CR_SERVER_GONE_ERROR
CR_UNKNOWN_ERROR
mysql_query()
int mysql_query(MYSQL *mysql, const char *query)
Executes the SQL query pointed to by the null-terminated string query.
The query must consist of a single SQL statement. You should not add
a terminating semicolon (`;') or \g to the statement.
mysql_query() cannot be used for queries that contain binary data; you
should use mysql_real_query() instead. (Binary data may contain the
`\0' character, which mysql_query() interprets as the end of the
query string.)
Zero if the query was successful. Non-zero if an error occurred.
CR_COMMANDS_OUT_OF_SYNC
CR_SERVER_GONE_ERROR
CR_SERVER_LOST
CR_UNKNOWN_ERROR
mysql_real_connect()
MYSQL *mysql_real_connect(MYSQL *mysql, const char *host,
const char *user, const char *passwd, const char *db,
unsigned int port, const char *unix_socket,
unsigned int client_flag)
mysql_real_connect() attempts to establish a connection to a
MySQL database engine running on host.
mysql_real_connect() must complete successfully before you can execute
any of the other API functions, with the exception of
mysql_get_client_info().
The parameters are specified as follows:
MYSQL
structure. Before calling mysql_real_connect() you must call
mysql_init() to initialize the MYSQL structure. See the
example below.
host may be either a hostname or an IP address. If
host is NULL or the string "localhost", a connection to
the local host is assumed. If the OS supports sockets (Unix) or named pipes
(Win32), they are used instead of TCP/IP to connect to the server.
user parameter contains the user's MySQL login ID. If
user is NULL, the current user is assumed. Under Unix, this is
the current login name. Under Windows ODBC, the current user name must be
specified explicitly.
See section 17.2 How to fill in the various fields in the ODBC administrator program.
passwd parameter contains the password for user. If
passwd is NULL, only entries in the user table for the
user that have a blank password field will be checked for a match. This
allows the database administrator to set up the MySQL privilege
system in such a way that users get different privileges depending on whether
or not they have specified a password.
Note: Do not attempt to encrypt the password before calling
mysql_real_connect(); password encryption is handled automatically by
the client API.
db is the database name.
If db is not NULL, the connection will set the default
database to this value.
port is not 0, the value will be used as the port number
for the TCP/IP connection. Note that the host parameter
determines the type of the connection.
unix_socket is not NULL, the string specifies the
socket or named pipe that should be used. Note that the host
parameter determines the type of the connection.
client_flag is usually 0, but can be set to a combination
of the following flags in very special circumstances:
| Flag name | Flag meaning |
CLIENT_FOUND_ROWS | Return the number of found (matched) rows, not the number of affected rows |
CLIENT_NO_SCHEMA | Don't allow the db_name.tbl_name.col_name syntax. This is for ODBC; It causes the parser to generate an error if you use that syntax, which is useful for trapping bugs in some ODBC programs.
|
CLIENT_COMPRESS | Use compression protocol |
CLIENT_ODBC | The client is an ODBC client. This changes
mysqld to be more ODBC-friendly.
|
A MYSQL* connection handle if the connection was successful.
NULL if the connection was unsuccessful. For a successful connection,
the return value is the same as the value of the first parameter, unless you
pass NULL for that parameter.
CR_CONN_HOST_ERROR
CR_CONNECTION_ERROR
CR_IPSOCK_ERROR
CR_OUT_OF_MEMORY
CR_SOCKET_CREATE_ERROR
CR_UNKNOWN_HOST
CR_VERSION_ERROR
--old-protocol option.
CR_NAMEDPIPEOPEN_ERROR;
CR_NAMEDPIPEWAIT_ERROR;
CR_NAMEDPIPESETSTATE_ERROR;
MYSQL mysql;
mysql_init(&mysql);
if (!mysql_real_connect(&mysql,"host","user","passwd","database",0,NULL,0))
{
fprintf(stderr, "Failed to connect to database: Error: %s\n",
mysql_error(&mysql));
}
mysql_real_query()
int mysql_real_query(MYSQL *mysql, const char *query, unsigned int length)
Executes the SQL query pointed to by query, which should be a string
length bytes long. The query must consist of a single SQL statement.
You should not add a terminating semicolon (`;') or \g to the
statement.
You must use mysql_real_query() rather than
mysql_query() for queries that contain binary data, since binary data
may contain the `\0' character. In addition, mysql_real_query()
is faster than mysql_query() since it does not call strlen() on
the query string.
Zero if the query was successful. Non-zero if an error occurred.
CR_COMMANDS_OUT_OF_SYNC
CR_SERVER_GONE_ERROR
CR_SERVER_LOST
CR_UNKNOWN_ERROR
mysql_reload()
int mysql_reload(MYSQL *mysql)
Asks the MySQL server to reload the grant tables. The connected user must have the reload privilege.
This function is deprecated. It is preferable to use mysql_query()
to issue a SQL FLUSH PRIVILEGES statement instead.
Zero for success. Non-zero if an error occurred.
CR_COMMANDS_OUT_OF_SYNC
CR_SERVER_GONE_ERROR
CR_SERVER_LOST
CR_UNKNOWN_ERROR
mysql_row_seek()
MYSQL_ROW_OFFSET mysql_row_seek(MYSQL_RES *result, MYSQL_ROW_OFFSET offset)
Sets the row cursor to an arbitrary row in a query result set. This requires
that the result set structure contains the entire result of the query, so
mysql_row_seek() may be used in conjunction only with
mysql_store_result(), not with mysql_use_result().
The offset should be a value returned from a call to mysql_row_tell()
or to mysql_row_seek(). This value is not simply a row number; if you
want to seek to a row within a result set using a row number, use
mysql_data_seek() instead.
The previous value of the row cursor. This value may be passed to a
subsequent call to mysql_row_seek().
None.
mysql_row_tell()
MYSQL_ROW_OFFSET mysql_row_tell(MYSQL_RES *result)
Returns the current position of the row cursor for the last
mysql_fetch_row(). This value can be used as an argument to
mysql_row_seek().
You should use mysql_row_tell() only after mysql_store_result(),
not after mysql_use_result().
The current offset of the row cursor.
None.
mysql_select_db()
int mysql_select_db(MYSQL *mysql, const char *db)
Causes the database specified by db to become the default (current)
database on the connection specified by mysql. In subsequent queries,
this database is the default for table references that do not include an
explicit database specifier.
mysql_select_db() fails unless the connected user can be authenticated
as having permission to use the database.
Zero for success. Non-zero if an error occurred.
CR_COMMANDS_OUT_OF_SYNC
CR_SERVER_GONE_ERROR
CR_SERVER_LOST
CR_UNKNOWN_ERROR
mysql_shutdown()
int mysql_shutdown(MYSQL *mysql)
Asks the database server to shutdown. The connected user must have shutdown privileges.
Zero for success. Non-zero if an error occurred.
CR_COMMANDS_OUT_OF_SYNC
CR_SERVER_GONE_ERROR
CR_SERVER_LOST
CR_UNKNOWN_ERROR
mysql_stat()
char *mysql_stat(MYSQL *mysql)
Returns a character string containing information similar to that provided by
the mysqladmin status command. This includes uptime in seconds and
the number of running threads, questions, reloads and open tables.
A character string describing the server status. NULL if an
error occurred.
CR_COMMANDS_OUT_OF_SYNC
CR_SERVER_GONE_ERROR
CR_SERVER_LOST
CR_UNKNOWN_ERROR
mysql_store_result()
MYSQL_RES *mysql_store_result(MYSQL *mysql)
You must call
mysql_store_result() or mysql_use_result() for every query
which successfully retrieves data (SELECT, SHOW,
DESCRIBE, EXPLAIN).
mysql_store_result() reads the entire result of a query to the client,
allocates a MYSQL_RES structure, and places the result into this
structure.
An empty result set is returned if there are no rows returned. (An empty
result set differs from a NULL return value.)
Once you have called mysql_store_result(), you may call
mysql_num_rows() to find out how many rows are in the result set.
You can call mysql_fetch_row() to fetch rows from the result set,
or mysql_row_seek() and mysql_row_tell() to obtain or
set the current row position within the result set.
You must call mysql_free_result() once you are done with the result
set.
See section 21.4.51 Why is it that after mysql_query() returns success, mysql_store_result() sometimes returns NULL?.
A MYSQL_RES result structure with the results. NULL if
an error occurred.
CR_COMMANDS_OUT_OF_SYNC
CR_OUT_OF_MEMORY
CR_SERVER_GONE_ERROR
CR_SERVER_LOST
CR_UNKNOWN_ERROR
mysql_thread_id()
unsigned long mysql_thread_id(MYSQL *mysql)
Returns the thread ID of the current connection. This value can be used as
an argument to mysql_kill() to kill the thread.
If the connection is lost and you reconnect with mysql_ping(), the
thread ID will change. This means you should not get the thread ID and store
it for later, you should get it when you need it.
The thread ID of the current connection.
None.
mysql_use_result()
MYSQL_RES *mysql_use_result(MYSQL *mysql)
You must call mysql_store_result() or mysql_use_result() for
every query which successfully retrieves data (SELECT, SHOW,
DESCRIBE, EXPLAIN).
mysql_use_result() initiates a result set retrieval but does not
actually read the result set into the client like mysql_store_result()
does. Instead, each row must be retrieved individually by making calls to
mysql_fetch_row(). This reads the result of a query directly from the
server without storing it in a temporary table or local buffer, which is
somewhat faster and uses much less memory than mysql_store_result().
The client will only allocate memory for the current row and a communication
buffer that may grow up to max_allowed_packet bytes.
On the other hand, you shouldn't use mysql_use_result() if you are
doing a lot of processing for each row on the client side, or if the output
is sent to a screen on which the user may type a ^S (stop scroll).
This will tie up the server and prevent other threads from updating any
tables from which the data are fetched.
When using mysql_use_result(), you must execute
mysql_fetch_row() until a NULL value is returned, otherwise the
unfetched rows will be returned as part of the result set for your next
query. The C API will give the error Commands out of sync; You can't
run this command now if you forget to do this!
You may not use mysql_data_seek(), mysql_row_seek(),
mysql_row_tell(), mysql_num_rows() or
mysql_affected_rows() with a result returned from
mysql_use_result(), nor may you issue other queries until the
mysql_use_result() has finished. (However, after you have fetched all
the rows, mysql_num_rows() will accurately return the number of rows
fetched.)
You must call mysql_free_result() once you are done with the result
set.
A MYSQL_RES result structure. NULL if an error occurred.
CR_COMMANDS_OUT_OF_SYNC
CR_OUT_OF_MEMORY
CR_SERVER_GONE_ERROR
CR_SERVER_LOST
CR_UNKNOWN_ERROR
mysql_query() returns success, mysql_store_result() sometimes returns NULL?
It is possible for mysql_store_result() to return NULL
following a successful call to mysql_query(). When this happens, it
means one of the following conditions occurred:
malloc() failure (for example, if the result set was too
large).
INSERT, UPDATE
or DELETE).
You can always check whether or not the statement should have produced a
non-empty result by calling mysql_field_count(). If
mysql_field_count() returns zero, the result is empty and the last
query was a statement that does not return values (for example, an
INSERT or a DELETE). If mysql_field_count() returns a
non-zero value, the statement should have produced a non-empty result.
See the description of the mysql_field_count() function for an
example.
You can test for an error by calling mysql_error() or
mysql_errno().
In addition to the result set returned by a query, you can also get the following information:
mysql_affected_rows() returns the number of rows affected by the last
query when doing an INSERT, UPDATE or DELETE. An
exception is that if DELETE is used without a WHERE clause, the
table is truncated, which is much faster! In this case,
mysql_affected_rows() returns zero for the number of records
affected.
mysql_num_rows() returns the number of rows in a result set. With
mysql_store_result(), mysql_num_rows() may be called as soon as
mysql_store_result() returns. With mysql_use_result(),
mysql_num_rows() may be called only after you have fetched all the
rows with mysql_fetch_row().
mysql_insert_id() returns the ID generated by the last
query that inserted a row into a table with an AUTO_INCREMENT index.
See section 21.4.29 mysql_insert_id().
LOAD DATA INFILE ..., INSERT INTO
... SELECT ..., UPDATE) return additional info. The result is
returned by mysql_info(). See the description for mysql_info()
for the format of the string that it returns. mysql_info() returns a
NULL pointer if there is no additional information.
If you insert a record in a table containing a column that has the
AUTO_INCREMENT attribute, you can get the most recently generated
ID by calling the mysql_insert_id() function.
You can also retrieve the ID by using the LAST_INSERT_ID() function in
a query string that you pass to mysql_query().
You can check if an AUTO_INCREMENT index is used by executing
the following code. This also checks if the query was an INSERT with
an AUTO_INCREMENT index:
if (mysql_error(&mysql)[0] == 0 &&
mysql_num_fields(result) == 0 &&
mysql_insert_id(&mysql) != 0)
{
used_id = mysql_insert_id(&mysql);
}
The most recently generated ID is maintained in the server on a
per-connection basis. It will not be changed by another client. It will not
even be changed if you update another AUTO_INCREMENT column with a
non-magic value (that is, a value that is not NULL and not 0).
If you want to use the ID that was generated for one table and insert it into a second table, you can use SQL statements like this:
INSERT INTO foo (auto,text)
VALUES(NULL,'text'); # generate ID by inserting NULL
INSERT INTO foo2 (id,text)
VALUES(LAST_INSERT_ID(),'text'); # use ID in second table
When linking with the C API, the following errors may occur on some systems:
gcc -g -o client test.o -L/usr/local/lib/mysql -lmysqlclient -lsocket -lnsl Undefined first referenced symbol in file floor /usr/local/lib/mysql/libmysqlclient.a(password.o) ld: fatal: Symbol referencing errors. No output written to client
If this happens on your system, you must include the math library by
adding -lm to the end of the compile/link line.
The client is ``almost'' thread-safe. The biggest problem is that the subroutines in `net.c' that read from sockets are not interrupt-safe. This was done with the thought that you might want to have your own alarm that can break a long read to a server.
The standard client libraries are not compiled with the thread options.
To get a thread-safe client, use the -lmysys, -lstring and
-ldbug libraries and net_serv.o that the server uses.
When using a threaded client, you can make great use of the routines in
the `thr_alarm.c' file. If you are using routines from the
mysys library, the only thing you must remember is to call
my_init() first!
All functions except mysql_real_connect() are currently thread-safe.
The following notes describe how to compile a thread-safe client library and
use it in a thread-safe manner. (The notes below for
mysql_real_connect() actually apply to mysql_connect() as well,
but since mysql_connect() is deprecated, you should be using
mysql_real_connect() anyway.)
To make mysql_real_connect() thread-safe, you must recompile the client
library with this command:
shell> CPPFLAGS=-DTHREAD_SAFE_CLIENT ./configure ...
You may get some errors because of undefined symbols when linking the standard client, because the pthread libraries are not included by default.
The resulting `libmysqlclient.a' library is now thread-safe. What this
means is that client code is thread-safe as long as two threads don't query
the same connection handle returned by mysql_real_connect() at the
same time; the client/server protocol allows only one request at a time on a
given connection. If you want to use multiple threads on the same
connection, you must have a mutex lock around your mysql_query() and
mysql_store_result() call combination. Once
mysql_store_result() is ready, the lock can be released and other
threads may query the same connection. (In other words, different threads
can use different MYSQL_RES pointers that were created with
mysql_store_result(), as long as they use the proper locking
protocol.) If you program with POSIX threads, you can use
pthread_mutex_lock() and pthread_mutex_unlock() to establish
and release a mutex lock.
If you used mysql_use_result() rather than mysql_store_result(),
the lock would need to surround mysql_use_result() and the calls
to mysql_fetch_row(). However, it really is best for threaded
clients not to use mysql_use_result().
This section documents the Perl DBI interface. The former interface
was called mysqlperl. Since DBI/DBD now is the
recommended Perl interface, mysqlperl is obsolete and is not
documented here.
DBI with DBD::mysql
DBI is a generic interface for many databases. That means that
you can write a script that works with many different database engines
without change. You need a DataBase Driver (DBD) defined for each
database type. For MySQL, this driver is called
DBD::mysql.
For more information on the Perl5 DBI, please visit the DBI web
page and read the documentation:
http://www.symbolstone.org/technology/perl/DBI/index.html
For more information on Object Oriented Programming (OOP) as defined in Perl5, see the Perl OOP page:
http://language.perl.com/info/documentation.html
Installation instructions for MySQL Perl support are given in section 4.10 Perl installation comments.
DBI interfacePortable DBI methods
connect | Establishes a connection to a database server |
disconnect | Disconnects from the database server |
prepare | Prepares a SQL statement for execution |
execute | Executes prepared statements |
do | Prepares and executes a SQL statement |
quote | Quotes string or BLOB values to be inserted
|
fetchrow_array | Fetches the next row as an array of fields. |
fetchrow_arrayref | Fetches next row as a reference array of fields |
fetchrow_hashref | Fetches next row as a reference to a hashtable |
fetchall_arrayref | Fetches all data as an array of arrays |
finish | Finishes a statement and let the system free resources |
rows | Returns the number of rows affected |
data_sources | Returns an array of databases available on localhost |
ChopBlanks | Controls whether fetchrow_* methods trim spaces
|
NUM_OF_PARAMS | The number of placeholders in the prepared statement |
NULLABLE | Which columns can be NULL
|
trace | Perform tracing for debugging |
MySQL-specific methods
insertid | The latest AUTO_INCREMENT value
|
is_blob | Which column are BLOB values
|
is_key | Which columns are keys |
is_num | Which columns are numeric |
is_pri_key | Which columns are primary keys |
is_not_null | Which columns CANNOT be NULL. See NULLABLE.
|
length | Maximum possible column sizes |
max_length | Maximum column sizes actually present in result |
NAME | Column names |
NUM_OF_FIELDS | Number of fields returned |
table | Table names in returned set |
type | All column types |
The Perl methods are described in more detail in the following sections. Variables used for method return values have these meanings:
$dbh
$sth
$rc
$rv
Portable DBI methods
connect($data_source, $username, $password)
connect method to make a database connection to the data
source. The $data_source value should begin with
DBI:driver_name:.
Example uses of connect with the DBD::mysql driver:
$dbh = DBI->connect("DBI:mysql:$database", $user, $password);
$dbh = DBI->connect("DBI:mysql:$database:$hostname",
$user, $password);
$dbh = DBI->connect("DBI:mysql:$database:$hostname:$port",
$user, $password);
If the user name and/or password are undefined, DBI uses the
values of the DBI_USER and DBI_PASS environment variables,
respectively. If you don't specify a hostname, it defaults to
'localhost'. If you don't specify a port number, it defaults to the
default MySQL port (3306).
As of Msql-Mysql-modules version 1.2009,
the $data_source value allows certain modifiers:
mysql_read_default_file=file_name
mysql_read_default_group=group_name
[client] group. By specifying the mysql_read_default_group
option, the default group becomes the [group_name] group.
mysql_compression=1
mysql_socket=/path/to/socket
DBI script, you can take them from the user's `~/.my.cnf'
option file instead by writing your connect call like this:
$dbh = DBI->connect("DBI:mysql:$database"
. ";mysql_read_default_file=$ENV{HOME}/.my.cnf",
$user, $password);
This call will read options defined for the [client] group in the
option file. If you wanted to do the same thing, but use options specified
for the [perl] group as well, you could use this:
$dbh = DBI->connect("DBI:mysql:$database"
. ";mysql_read_default_file=$ENV{HOME}/.my.cnf"
. ";mysql_read_default_group=perl",
$user, $password);
disconnect
disconnect method disconnects the database handle from the database.
This is typically called right before you exit from the program.
Example:
$rc = $dbh->disconnect;
prepare($statement)
($sth) which you can use to invoke
the execute method.
Typically you handle SELECT statements (and SELECT-like statements
such as SHOW, DESCRIBE and EXPLAIN) by means of
prepare and execute.
Example:
$sth = $dbh->prepare($statement)
or die "Can't prepare $statement: $dbh->errstr\n";
execute
execute method executes a prepared statement. For
non-SELECT statements, execute returns the number of rows
affected. If no rows are affected, execute returns "0E0",
which Perl treats as zero but regards as true. For SELECT statements,
execute only starts the SQL query in the database; you need to use one
of the fetch_* methods described below to retrieve the data.
Example:
$rv = $sth->execute
or die "can't execute the query: $sth->errstr;
do($statement)
do method prepares and executes a SQL statement and returns the
number of rows affected. If no rows are affected, do returns
"0E0", which Perl treats as zero but regards as true. This method is
generally used for non-SELECT statements which cannot be prepared in
advance (due to driver limitations) or which do not need to executed more
than once (inserts, deletes, etc.). Example:
$rv = $dbh->do($statement)
or die "Can't execute $statement: $dbh- >errstr\n";
quote($string)
quote method is used to "escape" any special characters contained in
the string and to add the required outer quotation marks.
Example:
$sql = $dbh->quote($string)
fetchrow_array
while(@row = $sth->fetchrow_array) {
print qw($row[0]\t$row[1]\t$row[2]\n);
}
fetchrow_arrayref
while($row_ref = $sth->fetchrow_arrayref) {
print qw($row_ref->[0]\t$row_ref->[1]\t$row_ref->[2]\n);
}
fetchrow_hashref
while($hash_ref = $sth->fetchrow_hashref) {
print qw($hash_ref->{firstname}\t$hash_ref->{lastname}\t\
$hash_ref- > title}\n);
}
fetchall_arrayref
my $table = $sth->fetchall_arrayref
or die "$sth->errstr\n";
my($i, $j);
for $i ( 0 .. $#{$table} ) {
for $j ( 0 .. $#{$table->[$i]} ) {
print "$table->[$i][$j]\t";
}
print "\n";
}
finish
$rc = $sth->finish;
rows
SELECT execute
statement. Example:
$rv = $sth->rows;
NULLABLE
NULL values.
Example:
$null_possible = $sth->{NULLABLE};
NUM_OF_FIELDS
SELECT or SHOW FIELDS
statement. You may use this for checking whether a statement returned a
result: A zero value indicates a non-SELECT statement like
INSERT, DELETE or UPDATE.
Example:
$nr_of_fields = $sth->{NUM_OF_FIELDS};
data_sources($driver_name)
'localhost'.
Example:
@dbs = DBI->data_sources("mysql");
ChopBlanks
fetchrow_* methods will chop
leading and trailing blanks from the returned values.
Example:
$sth->{'ChopBlanks'} =1;
trace($trace_level)
trace($trace_level, $trace_filename)
trace method enables or disables tracing. When invoked as a
DBI class method, it affects tracing for all handles. When invoked as
a database or statement handle method, it affects tracing for the given
handle (and any future children of the handle). Setting $trace_level
to 2 provides detailed trace information. Setting $trace_level to 0
disables tracing. Trace output goes to the standard error output by
default. If $trace_filename is specified, the file is opened in
append mode and output for all traced handles is written to that
file. Example:
DBI->trace(2); # trace everything DBI->trace(2,"/tmp/dbi.out"); # trace everything to /tmp/dbi.out $dth->trace(2); # trace this database handle $sth->trace(2); # trace this statement handleYou can also enable
DBI tracing by setting the DBI_TRACE
environment variable. Setting it to a numeric value is equivalent to calling
DBI->(value). Setting it to a pathname is equivalent to calling
DBI->(2,value).
MySQL-specific methods
The methods shown below are MySQL-specific and not part of the
DBI standard. Several of them are now deprecated:
is_blob, is_key, is_num, is_pri_key,
is_not_null, length, max_length, and table.
Where DBI-standard alternatives exist, they are noted below.
insertid
AUTO_INCREMENT feature of MySQL, the new
auto-incremented values will be stored here.
Example:
$new_id = $sth->{insertid};
As an alternative, you can use $dbh->{'mysql_insertid'}.
is_blob
BLOB.
Example:
$keys = $sth->{is_blob};
is_key
$keys = $sth->{is_key};
is_num
$nums = $sth->{is_num};
is_pri_key
$pri_keys = $sth->{is_pri_key};
is_not_null
NULL
values.
Example:
$not_nulls = $sth->{is_not_null};
is_not_null is deprecated; it is preferable to use the
NULLABLE attribute (described above), since that is a DBI standard.
length
max_length
length array indicates the maximum possible sizes that each column may
be (as declared in the table description). The max_length array
indicates the maximum sizes actually present in the result table. Example:
$lengths = $sth->{length};
$max_lengths = $sth->{max_length};
NAME
$names = $sth->{NAME};
table
$tables = $sth->{table};
type
$types = $sth->{type};
DBI/DBD information
You can use the perldoc command to get more information about
DBI.
perldoc DBI perldoc DBI::FAQ perldoc DBD::mysql
You can also use the pod2man, pod2html, etc., tools to
translate to other formats.
And of course you can find the latest DBI information at
the DBI web page:
http://www.symbolstone.org/technology/perl/DBI/index.html
The MySQL Contrib directory contains an Eiffel wrapper written by Michael Ravits.
You can also find this at: http://www.netpedia.net/hosting/newplayer/
There are 2 supported JDBC drivers for MySQL (the twz and mm driver). You can find a copy of these at http://www.mysql.com/Contrib. For documentation consult any JDBC documentation and the drivers own documentation for MySQL specific features.
PHP is a server-side, HTML embedded scripting language that may be used to create dynamic web pages. It contains support for accessing several databases, including MySQL. PHP may be run as a separate program, or compiled as a module for use with the Apache web server.
The distribution and documentation are available at the PHP website.
MySQL support. This is described in
detail in the PHP manual.
Two API's are available in the MySQL Contrib directory.
The MySQL Contrib directory contains a Python interface written by Joseph Skinner.
You can also use the Python interface to iODBC to access a MySQL server. mxODBC
TCL at binevolve. The Contrib directory contains a TCL interface that is based on msqltcl 1.50.
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