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@setfilename prepare.info

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@settitle MySQL Prepared Statements

@c We want single-sided heading format, with chapters on new pages. To
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@c  @titlepage
@c @sp 10
@c @center @titlefont{MySQL Prepared Statements}
@c @sp 10
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@c blank page after title page makes page 1 be a page front.
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@iftex
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@c @node Top, MySQL C API, (dir), (dir)

@c @menu
@c * MySQL C API::                 
@c @end menu

@c @node MySQL C API,  , Top, Top
@c @chapter MySQL C API

@c @menu
@c * Prepared statements::         
@c @end menu

@node Top, MySQL prepared statements, (dir), (dir)

@menu
* MySQL prepared statements::   
@end menu

@node MySQL prepared statements,  , Top, Top
@chapter MySQL Prepared Statements

@menu
* C Prepared statements::       
* C Prepared statement datatypes::  
* C Prepared statements function overview::  
* C Prepared statement functions::  
@end menu

@node C Prepared statements, C Prepared statement datatypes, MySQL prepared statements, MySQL prepared statements
@subsection C Prepared Statements

@sp 1

From MySQL 4.1 and above, you can also make use of the prepared
statements using the statement handler 'MYSQL_STMT', which supports
simultanious query executions along with input and output binding.

@sp 1

Prepared execution is an efficient way to execute a statement more than
once. The statement is first parsed, or prepared. This is executed one
or more times at a later time using the statement handle that is
returned during the prepare.

@sp 1

Another advantage of prepared statements is that, it uses a binary protocol
which makes the data tranfer between client and server in a more efficient
way than the old MySQL protocol.

@sp 1

Prepared execution is faster than direct execution for statements
executed more than once, primarly becuase the query is parsed only
once; In the case of direct execution, the query is parsed every
time. Prepared execution also can provide a reduction in the network
traffic becuase during the execute call, it only sends the data for the
parameters.



@node C Prepared statement datatypes, C Prepared statements function overview, C Prepared statements, MySQL prepared statements
@subsection C Prepared Statements DataTypes

Prepared statements mainly uses the following two @code{MYSQL_STMT} and
@code{MYSQL_BIND} structures:
@sp 1

@table @code
@tindex MYSQL C type
@item MYSQL_STMT
This structure represents a statement handle to prepared statements.It
is used for all statement related functions. 

@sp 1 

The statement is initialized when the query is prepared using 
@code{mysql_prepare()}.

@sp 1 

One connection can have 'n' statement handles, and the limit depends up on
the system resources.

@sp 1

@tindex MYSQL_BIND C type
@item MYSQL_BIND
This structure is used in order to bind parameter buffers inorder to
send the parameters data to @code{mysql_execute()} call; as well as to
bind row buffers to fetch the result set data using @code{mysql_fetch()}.
@end table

@sp 1

@noindent
The @code{MYSQL_BIND} structure contains the members listed here:


@table @code
@item enum enum_field_types buffer_type [input]
The type of the buffer. The @code{type} value must be one of the following:


@itemize @bullet
@item @code{MYSQL_TYPE_TINY}
@item @code{MYSQL_TYPE_SHORT}
@item @code{MYSQL_TYPE_LONG}  
@item @code{MYSQL_TYPE_LONGLONG}
@item @code{MYSQL_TYPE_FLOAT}
@item @code{MYSQL_TYPE_DOUBLE}
@item @code{MYSQL_TYPE_STRING}
@item @code{MYSQL_TYPE_VAR_STRING}
@item @code{MYSQL_TYPE_TINY_BLOB}
@item @code{MYSQL_TYPE_MEDIUM_BLOB}
@item @code{MYSQL_TYPE_LONG_BLOB}
@item @code{MYSQL_TYPE_BLOB}
@end itemize
@sp 1

@item void *buffer [input/output]
A pointer to a buffer for the parameters data in case if it is used to
supply parameters data or pointer to a buffer in which to return the
data when the structure is used for result set bind.

@sp 1

@item long *length [input/output]
Pointer to the buffer for the parameter's length. When the structure is
used as a input parameter data binding, then this argument points to a
buffer that, when @code{mysql_execute()} is called, contains one of the 
following:

@itemize @bullet
@item
The length of the parameter value stored in *buffer. This is ignored
except for character or binary C data.
@item 
MYSQL_NULL_DATA. The parameter value is NULL.
@item
MYSQL_LONG_DATA. The parameter value is a long data and is supplied in
chunks through @code{mysql_send_long_data()}.
@end itemize

If the length is a null pointer, then the protocol assumes that all
input parameter values are non-NULL and that character and binary data
are null terminated.


When this structure is used in output binding, then @code{mysql_fetch()}
return the following values in the length buffer:

@itemize @bullet
@item
The length of the data that is returned
@item
MYSQL_NULL_DATA, indicating the data returned is a NULL data.
@end itemize


@c @item bool is_null [input]
@c To indicate the parameter data is NULL. This is same as supplying
@c MYSQL_NULL_DATA, -1 as the length in length pointer.


@c @item bool is_long_data [input]
@c To indicate the parameter data is a long data, and the data will be
@c supplied in chunks through @code{mysql_send_long_data()}.This is also
@c same as supplying MYSQL_LONG_DATA, -2 as the length in length pointer.
@c @end table
@end table


@node C Prepared statements function overview, C Prepared statement functions, C Prepared statement datatypes, MySQL prepared statements
@subsection C Prepared Statements Function Overview

@cindex C Prepared statements API, functions
@cindex functions, C Prepared statements API

The functions available in the prepared statements are listed here and
are described in greater detail in the later section.
@xref{C Prepared statement functions}.

@multitable @columnfractions .32 .68
@item @strong{Function} @tab @strong{Description}

@item @strong{mysql_prepare()} @tab Prepares an SQL string for execution.

@item @strong{mysql_param_count()} @tab Returns the number of parameters in a prepared SQL statement.

@item @strong{mysql_prepare_result()} @tab Returns prepared statement meta information in the form of resultset.

@item @strong{mysql_bind_param()} @tab Binds a buffer to parameter markers in a prepared SQL statement.

@item @strong{mysql_execute()} @tab Executes the prepared statement.

@item @strong{mysql_stmt_affected_rows()} @tab Returns the number of rows changes/deleted/inserted by the last UPDATE,DELETE,or INSERT query

@item @strong{mysql_bind_result()} @tab Binds application data buffers to columns in the resultset.

@item @strong{mysql_fetch()} @tab Fetches the next rowset of data from the result set and returns data for all bound columns.

@item @strong{mysql_stmt_close()} @tab Frees memory used by prepared statement.

@item @strong{mysql_stmt_errno()} @tab Returns the error number for the last statement execution.

@item @strong{mysql_stmt_error()} @tab Returns the error message for the last statement execution.

@item @strong{mysql_send_long_data()} @tab Sends long data in chunks to server.

@c TO BE MOVED TO MAIN C API FUCTIONS
@item @strong{mysql_commit()} @tab Commits the transaction.

@item @strong{mysql_rollback()} @tab Rollbacks the transaction.

@item @strong{mysql_autocommit()} @tab Toggles the autocommit mode to on/off.

@item @strong{mysql_more_results()} @tab Returns if there are any more results exists

@item @strong{mysql_next_result()} @tab Returns/Initiates the next result in the multi-query executions

@end multitable

@sp 1
Call @code{mysql_prepare()} to prepare and initialize the statement
handle, then call @code{mysql_bind_param()} to supply the parameters
data, and then call @code{mysql_execute()} to execute the query. You can
repeat the @code{mysql_execute()} by changing parameter values from the
respective buffer supplied through @code{mysql_bind_param()}.

@sp 1


In case if the query is a SELECT statement or any other query which
results in a resultset, then mysql_prepare() will also return the result
set meta data information in the form of @code{MYSQL_RES } result set 
through @code{mysql_prepare_result()}.

@sp 1

You can supply the result buffers using @code{mysql_bind_result()}, so
that the @code{mysql_fetch()} will automatically returns data to this
buffers. This is row by row fetching.

@sp 1

You can also send the text or binary data in chunks to server using
@code{mysql_send_long_data()}, by specifying the option is_long_data=1
or length=MYSQL_LONG_DATA or -2 in the MYSQL_BIND structure supplied 
with @code{mysql_bind_param()}.

@sp 1

Once the statement execution is over, it must be freed using
@code{mysql_stmt_close} so that it frees all the alloced resources for
the statement handle.


@subsubheading Execution Steps:

To prepare and execute a statement, the application:

@itemize @bullet
@item
Calls @strong{mysql_prepare()} and passes it a string containing the SQL
statement. On a successful prepare, mysql_prepare returns the valid statement
handle back to the application
@item
If the query results in a resultset, then @strong{mysql_prepare_result}
returns the result set meta info..
@item
Sets the values of any parameters using @strong{mysql_bind_param}. All
parameters must be set; else it will return an error or produce
un-expected results
@item
Calls @strong{mysql_execute} to execute the statement.
@item
Repeat steps 2 and 3 as necessary, by changing the parameter values and
re-executing the statement.
@item
Bind the data buffers to return the row values, if it is a result set
query; using @strong{mysql_bind_result()}.
@item
Fetch the data to buffers row by row by calling @strong{mysql_fetch()}
repetedely until no more rows found.
@item
When @strong{mysql_prepare()} is called, in the MySQL client/server protocol:
@itemize @minus
@item
Server parses the query and sends the ok status back to client by
assinging a statement id. It also sends total number of parameters,
columns count and its meta information if it is a result set oriented
query. All syntax and symantecs of the query is checked during this call
by the server.
@item
Client uses this statement id for the further executions, so that server
identifies the statement back from the pool of statements. Now, client
allocates a statement handle with this id and returns back to
application.
@end itemize
@item
When @strong{mysql_execute()} is called, in the MySQL client/server protocol:
@itemize @minus
@item
Client uses the statement handle and sends the parameters data to
server.
@item
Server identifies the statement using the id provided by the client, and
replaces the parameter markers with the newly supplied data and executes
the query. If it results in a result set, then sends the data back to
client, else sends an OK status with total number of rows
changes/deleted/inserted.
@end itemize
@item
When @strong{mysql_fetch()} is called, in the MySQL client/server protocol:
@itemize @minus
@item
Client reads the data from the packet row by row and places it to
application data buffers by doing the necessary conversions. If the
application buffer type is same as that of field type, then the
conversions are stright forward.
@end itemize
@end itemize



You can get the statement error code and message using
@code{mysql_stmt_errno()} and @code{mysql_stmt_error()} respectively.


@node C Prepared statement functions,  , C Prepared statements function overview, MySQL prepared statements
@subsection C Prepared Statement Function Descriptions

You need to use the following functions when you want to prepare and
execute the queries.


@menu
* mysql_prepare::               
* mysql_param_count::           
* mysql_prepare_result::        
* mysql_bind_param::            
* mysql_execute::               
* mysql_stmt_affected_rows::    
* mysql_bind_result::           
* mysql_fetch::                 
* mysql_send_long_data::        
* mysql_stmt_close::            
* mysql_stmt_errno::            
* mysql_stmt_error::            
* mysql_commit::                
* mysql_rollback::              
* mysql_autocommit::            
@end menu

@node mysql_prepare, mysql_param_count, C Prepared statement functions, C Prepared statement functions
@subsubsection @code{mysql_prepare()}

@findex @code{mysql_prepare()}

@code{MYSQL_STMT * mysql_prepare(MYSQL *mysql, const char *query, unsigned
long length)}

@subsubheading Description

Prepares 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.

@sp 1
The application can include one or more parameter markers in the SQL
statement. To include a parameter marker, the appication embeds a
question mark (@code{?}) into the SQL string at the appropriate
position. 

@sp 1
The markers are legal only in certain places in SQL statements. For
example, they are not allowed in the select list(the list of columns to
be returned by a SELECT statement), nor are they allowed as both
operands of a binary operator such as the equal sign (=), becuase it
would be impossible to determine the parameter type. In general,
parameters are legal only in Data Manipulation Languange(DML)
statements, and not in Data Defination Language(DDL) statements.

@sp 1
The parameter markers are then bound to application variables using
@code{mysql_bind_param()}.



@subsubheading Return Values

@code{MYSQL_STMT} if the prepare was successful. NULL if an error
occured.

@subsubheading Errors

If the prepare is not successful, i.e. when @code{mysql_prepare()} returned a
NULL statement, errors can be obtained by calling @code{mysql_error()}. 


@subsubheading Example

For the usage of @code{mysql_prepare()} refer to the Example from
@ref{mysql_execute,mysql_execute()}.




@node mysql_param_count, mysql_prepare_result, mysql_prepare, C Prepared statement functions
@subsubsection @code{mysql_param_count()}

@findex @code{mysql_param_count()}

@code{unsigned int mysql_param_count(MYSQL_STMT *stmt)}

@subsubheading Description

Returns the number of parameter markers present from the prepared query.

@subsubheading Return Values

An unsigned integer representing the number of parameters in a
statement.

@subsubheading Errors

None

@subsubheading Example

For the usage of @code{mysql_param_count()} refer to the Example from
@ref{mysql_execute,mysql_execute()}.



@node mysql_prepare_result, mysql_bind_param, mysql_param_count, C Prepared statement functions
@subsubsection @code{mysql_prepare_result()}


@findex @code{mysql_prepare_result}.

@code{MYSQL_RES *mysql_prepare_result(MYSQL_STMT *stmt)}

@subsubheading Description

If the @code{mysql_prepare()} resulted in a result set query, then
@code{mysql_prepare_result()} returns the result set meta data in the form of
@code{MYSQL_RES} structure; which can further be used to process the
meta information such as total number of fields and individual field
information. This resulted result set can be passed as an argument to
any of the field based APIs in order to process the result set meta data 
information such as:

@itemize @minus
@item
mysql_num_fields()
@item 
mysql_fetch_field()
@item
mysql_fetch_field_direct()
@item
mysql_fetch_fields()
@item
mysql_field_count()
@item
mysql_field_seek()
@item
mysql_field_tell() and
@item
mysql_free_result()
@end itemize


@subsubheading Return Values

A @code{MYSQL_RES} result structure. NULL if no meta information exists from
the prepared query.


@subsubheading Errors

None


@subsubheading Example

For the usage of @code{mysql_prepare_result()} refer to the Example from
@ref{mysql_fetch,mysql_fetch()}



@node mysql_bind_param, mysql_execute, mysql_prepare_result, C Prepared statement functions
@subsubsection @code{mysql_bind_param()}

@findex @code{mysql_bind_param()}

@code{int mysql_bind_param(MYSQL_STMT *stmt, MYSQL_BIND *bind)}

@subsubheading Description

@code{mysql_bind_param} is used to bind data for the parameter markers
in the SQL statement from @code{mysql_prepare}. It uses the structure
MYSQL_BIND to supply the data.
 
The supported buffer types are:

@itemize @bullet
@item
MYSQL_TYPE_TINY
@item
MYSQL_TYPE_SHORT
@item
MYSQL_TYPE_LONG
@item
MYSQL_TYPE_LONGLONG
@item
MYSQL_TYPE_FLOAT
@item
MYSQL_TYPE_DOUBLE
@item
MYSQL_TYPE_STRING
@item
MYSQL_TYPE_VAR_STRING
@item
MYSQL_TYPE_TINY_BLOB
@item
MYSQL_TYPE_MEDIUM_BLOB
@item
MYSQL_TYPE_LONG_BLOB
@end itemize

@subsubheading Return Values

Zero if the bind was successful. Non-zero if an error occured.

@subsubheading Errors
@table @code
@item CR_NO_PREPARE_STMT
No prepared statement exists
@item CR_NO_PARAMETERS_EXISTS
No parameters exists to bind
@item CR_INVALID_BUFFER_USE
Indicates if the bind is to supply the long data in chunks and if the
buffer type is non string or binary
@item CR_UNSUPPORTED_PARAM_TYPE
The conversion is not supported, possibly the buffer_type is illegal or
its not from the above list of supported types.
@end table

@subsubheading Example

For the usage of @code{mysql_bind_param()} refer to the Example from
@ref{mysql_execute,mysql_execute()}.



@node mysql_execute, mysql_stmt_affected_rows, mysql_bind_param, C Prepared statement functions
@subsubsection @code{mysql_execute()}

@findex @code{mysql_execute()}

@code{int mysql_execute(MYSQL_STMT *stmt}.

@subsubheading Description

@code{mysql_execute()} executes the prepared query associated with the
statement handle. The parameter marker values will be sent to server
during this call, so that server replaces markers with this newly
supplied data.

@sp 1

If the statement is UPDATE,DELETE,or INSERT, the total number of
changed/deletd/inserted values can be found by calling
@code{mysql_stmt_affected_rows}. If this is a result set query, then one
must call @code{mysql_fetch()} to fetch the data prior to calling any
other calls which results in query processing. For more information on
how to fetch the statement binary data, refer to @ref{mysql_fetch}.
 

@subsubheading Return Values

@code{mysql_execute()} returns the following return values:

@multitable @columnfractions .30 .65
@item @strong{Return Value}         @tab @strong{Description}
@item MYSQL_SUCCESS,      0            @tab Successful
@item MYSQL_STATUS_ERROR, 1            @tab Error occured. Error code and
message can be obtained by calling @code{mysql_stmt_errno()} and @code{mysql_stmt_error()}.
@item MYSQL_NEED_DATA,    99           @tab One of the parameter buffer is
indicating the data suppy in chunks, and the supply is not yet complete.
@end multitable


@subsubheading Errors

@table @code
@item CR_NO_PREPARE_QUERY
No query prepared prior to execution
@item CR_ALL_PARAMS_NOT_BOUND
Not all parameters data is supplied
@item CR_SERVER_GONE_ERROR
The MySQL server has gone away
@item CR_UNKNOWN_ERROR
An unkown error occured
@end table


@subsubheading Example

The following example explains the uasage of @code{mysql_prepare},
@code{mysql_param_count}, @code{mysql_bind_param}, @code{mysql_execute}
and @code{mysql_stmt_affected_rows()}.

@example

MYSQL_BIND   bind[3];
MYSQL_STMT   *stmt;
ulonglong    affected_rows;
long         length;
unsigned int param_count;
int          int_data;
char         str_data[50], query[255];

  /* Set autocommit mode to true */
  mysql_autocommit(mysql, 1);
  
  if (mysql_query(mysql,"DROP TABLE IF EXISTS test_table"))
  @{
    fprintf(stderr, "\n drop table failed");
    fprintf(stderr, "\n %s", mysql_error(mysql));
    exit(0);
  @}
  if (mysql_query(mysql,"CREATE TABLE test_table(col1 int, col2 varchar(50), \
                                                 col3 smallint,\
                                                 col4 timestamp(14))"))
  @{
    fprintf(stderr, "\n create table failed");
    fprintf(stderr, "\n %s", mysql_error(mysql));
    exit(0);
  @}
  
  /* Prepare a insert query with 3 parameters */
  strcpy(query, "INSERT INTO test_table(col1,col2,col3) values(?,?,?)");
  if(!(stmt = mysql_prepare(mysql,query,strlen(query))))
  @{
    fprintf(stderr, "\n prepare, insert failed");
    fprintf(stderr, "\n %s", mysql_error(mysql));
    exit(0);
  @}
  fprintf(stdout, "\n prepare, insert successful");

  /* Get the parameter count from the statement */
  param_count= mysql_param_count(stmt);

  fprintf(stdout, "\n total parameters in insert: %d", param_count);
  if (param_count != 3) /* validate parameter count */
  @{
    fprintf(stderr, "\n invalid parameter count returned by MySQL");
    exit(0);
  @}

  /* Bind the data for the parameters */

  /* INTEGER PART */
  memset(bind,0,sizeof(bind));
  bind[0].buffer_type= MYSQL_TYPE_LONG;
  bind[0].buffer= (void *)&int_data;
 
  /* STRING PART */
  bind[1].buffer_type= MYSQL_TYPE_VAR_STRING;
  bind[1].buffer= (void *)str_data;
  bind[1].buffer_length= sizeof(str_data);
 
  /* SMALLINT PART */
  bind[2].buffer_type= MYSQL_TYPE_SHORT;
  bind[2].buffer= (void *)&small_data;       
  bind[2].length= (long *)&length;

  /* Bind the buffers */
  if (mysql_bind_param(stmt, bind))
  @{
    fprintf(stderr, "\n param bind failed");
    fprintf(stderr, "\n %s", mysql_stmt_error(stmt));
    exit(0);
  @}

  /* Specify the data */
  int_data= 10;             /* integer */
  strcpy(str_data,"MySQL"); /* string  */
  /* INSERT SMALLINT data as NULL */
  length= MYSQL_NULL_DATA;

  /* Execute the insert statement - 1*/
  if (mysql_execute(stmt))
  @{
    fprintf(stderr, "\n execute 1 failed");
    fprintf(stderr, "\n %s", mysql_stmt_error(stmt));
    fprintf(stderr, "\n send a bug report to bugs@@lists.mysql.com, by asking why this is not working ?");
    exit(0);
  @}
    
  /* Get the total rows affected */   
  affected_rows= mysql_stmt_affected_rows(stmt);

  fprintf(stdout, "\n total affected rows: %lld", affected_rows);
  if (affected_rows != 1) /* validate affected rows */
  @{
    fprintf(stderr, "\n invalid affected rows by MySQL");
    exit(0);
  @}

  /* Re-execute the insert, by changing the values */
  int_data= 1000;             
  strcpy(str_data,"The most popular open source database"); 
  small_data= 1000;         /* smallint */
  length= 0;

  /* Execute the insert statement - 2*/
  if (mysql_execute(stmt))
  @{
    fprintf(stderr, "\n execute 2 failed");
    fprintf(stderr, "\n %s", mysql_stmt_error(stmt));
    exit(0);
  @}
    
  /* Get the total rows affected */   
  affected_rows= mysql_stmt_affected_rows(stmt);

  fprintf(stdout, "\n total affected rows: %lld", affected_rows);
  if (affected_rows != 1) /* validate affected rows */
  @{
    fprintf(stderr, "\n invalid affected rows by MySQL");
    exit(0);
  @}

  /* Close the statement */
  if (mysql_stmt_close(stmt))
  @{
    fprintf(stderr, "\n failed while closing the statement");
    fprintf(stderr, "\n %s", mysql_stmt_error(stmt));
    exit(0);
  @}
  
  /* DROP THE TABLE */
  if (mysql_query(mysql,"DROP TABLE test_table"))
  @{
    fprintf(stderr, "\n drop table failed");
    fprintf(stderr, "\n %s", mysql_error(mysql));
    exit(0);
  @}
  fprintf(stdout, "Success, MySQL prepared statements are working great !!!");
@end example




@node mysql_stmt_affected_rows, mysql_bind_result, mysql_execute, C Prepared statement functions
@subsubsection @code{mysql_stmt_affected_rows()}

@findex @code{mysql_stmt_affected_rows()}

@code{ulonglong mysql_stmt_affected_rows(MYSQL_STMT *stmt)}

@subsubheading Description

Returns total number of rows changed by the last execute statement. May
be called immediatlely after mysql_execute() for UPDATE,DELETE,or INSERT
statements.For SELECT statements, mysql_stmt_affected rows works like
mysql_num_rows().

@subsubheading Return Values

An integer greater than zero indicates the number of rows affected or
retrieved. Zero indicates that no records where updated for an UPDATE 
statement, no rows 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_stmt_affected_rows() was called 
prior to calling mysql_fetch(). 

@subsubheading Errors

None.

@subsubheading Example

For the usage of @code{mysql_stmt_affected_rows()} refer to the Example
from @ref{mysql_execute,mysql_execute()}.





@node mysql_bind_result, mysql_fetch, mysql_stmt_affected_rows, C Prepared statement functions
@subsubsection @code{mysql_bind_result()}

@findex @code{mysql_bind_result()}

@code{my_bool mysql_bind_result(MYSQL_STMT *stmt, MYSQL_BIND *bind)}

@subsubheading Description

@code{mysql_bind_result()} is ised to associate, or bind, columns in the
resultset to data buffers and length buffers. When @code{mysql_fetch()} is
called to fetch data, the MySQL client protocol returns the data for the
bound columns in the specified buffers.

@sp 1

Note that all columns must be bound prior to calling @code{mysql_fetch()}
in case of fetching the data to buffers; else @code{mysql_fetch()} simply ignores
the data fetch; also the buffers should be sufficient enough to hold the
data as the ptotocol doesn't return the data in chunks.

@sp 1

A column can be bound or rebound at any time, even after data has been
fetched from the result set. The new binding takes effect the next time
@code{mysql_fetch()} is called. For example, suppose an application binds
the columns in a result set and calls @code{mysql_fetch()}. The mysql
protocol returns data in the bound buffers. Now suppose the application
binds the columns to a different set of buffers, then the protocol does
not place the data for the just fetched row in the newly bound
buffers. Instead, it does when the next @code{mysql_fetch()} is called.

@sp 1

To bind a column, an application calls @code{mysql_bind_result()} and
passes the type, address, and the address of the length buffer.
 
The supported buffer types are:

@itemize @bullet
@item
MYSQL_TYPE_TINY
@item
MYSQL_TYPE_SHORT
@item
MYSQL_TYPE_LONG
@item
MYSQL_TYPE_LONGLONG
@item
MYSQL_TYPE_FLOAT
@item
MYSQL_TYPE_DOUBLE
@item
MYSQL_TYPE_STRING
@item
MYSQL_TYPE_VAR_STRING
@item
MYSQL_TYPE_BLOB
@item
MYSQL_TYPE_TINY_BLOB
@item
MYSQL_TYPE_MEDIUM_BLOB
@item
MYSQL_TYPE_LONG_BLOB
@end itemize

@subsubheading Return Values

Zero if the bind was successful. Non-zero if an error occured.

@subsubheading Errors
@table @code
@item CR_NO_PREPARE_STMT
No prepared statement exists
@item CR_UNSUPPORTED_PARAM_TYPE
The conversion is not supported, possibly the buffer_type is illegal or
its not from the list of supported types.
@end table

@subsubheading Example

For the usage of @code{mysql_bind_result()} refer to the Example from
@ref{mysql_fetch,mysql_fetch()}



@node mysql_fetch, mysql_send_long_data, mysql_bind_result, C Prepared statement functions
@subsubsection @code{mysql_fetch()}

@findex code{mysql_fetch()}

@code{int mysql_fetch(MYSQL_STMT *stmt)}

@subsubheading Description

@code{mysql_fetch()} returns the next rowset in the result set. It can
be called only while the result set exists i.e. after a call to
@code{mysql_execute()} that creates a result set.

@sp 1

If row buffers are bound using @code{mysql_bind_result()}, it returns
the data in those buffers for all the columns in the current row
set and the lengths are returned to the length pointer.

@sp 1
Note that, all columns must be bound by the application.

@sp 1
If the data fetched is a NULL data, then the length buffer will have a
value of @strong{MYSQL_NULL_DATA}, -1, else it will have the length of
the data being fetched based on the buffer type specified by the
application. All numeric, float and double types have the
fixed length(in bytes) as listed below:

@multitable @columnfractions .10 .30
@item @strong{Type}           @tab @strong{Length} 
@item MYSQL_TYPE_TINY         @tab 1
@item MYSQL_TYPE_SHORT        @tab 2
@item MYSQL_TYPE_LONG         @tab 4
@item MYSQL_TYPE_FLOAT        @tab 4
@item MYSQL_TYPE_LONGLONG     @tab 8
@item MYSQL_TYPE_DOUBLE       @tab 8
@item MYSQL_TYPE_STRING       @tab data length
@item MYSQL_TYPE_VAR_STRING   @tab data_length
@item MYSQL_TYPE_BLOB         @tab data_length
@item MYSQL_TYPE_TINY_BLOB    @tab data_length
@item MYSQL_TYPE_MEDIUM_BLOB  @tab data_length
@item MYSQL_TYPE_LONG_BLOB    @tab data_length
@end multitable

@*
where @code{*data_length} is nothing but the 'Actual length of the data'.

@subsubheading Return Values

@multitable @columnfractions .30 .65
@item @strong{Return Value}         @tab @strong{Description}
@item MYSQL_SUCCESS,      0            @tab Successful, the data has been
fetched to application data buffers.
@item MYSQL_STATUS_ERROR, 1            @tab Error occured. Error code and
message can be obtained by calling @code{mysql_stmt_errno()} and @code{mysql_stmt_error()}.
@item MYSQL_NO_DATA,      100           @tab No more rows/data exists
@end multitable


@subsubheading Errors
@table @code
@item CR_UNSUPPORTED_PARAM_TYPE
If the field type is DATE,DATETIME,TIME,or TIMESTAMP; and the
application buffer type is non string based.
@item
All other un-supported conversions are returned from
@code{mysql_bind_result()}.
@end table

@subsubheading Example

The following example explains the usage of @code{mysql_prepare_result},
@code{mysql_bind_result()}, and @code{mysql_fetch()}

@example
  
MYSQL_STMT *stmt;  
MYSQL_BIND bind[2];
MYSQL_RES  *result;
int        int_data;
long       int_length, str_length;
char       str_data[50];

  query= "SELECT col1, col2 FROM test_table WHERE col1= 10)");
  if (!(stmt= mysql_prepare(&mysql, query, strlen(query)))
  @{
    fprintf(stderr, "\n prepare failed");
    fprintf(stderr, "\n %s", mysql_error(&stmt));
    exit(0);
  @}

  /* Get the fields meta information */
  if (!(result= mysql_prepare_result(stmt)))
  @{
    fprintf(stderr, "\n prepare_result failed");
    fprintf(stderr, "\n %s", mysql_stmt_error(stmt));
    exit(0);
  @}

  fprintf(stdout, "Total fields: %ld", mysql_num_fields(result));

  if (mysql_num_fields(result) != 2)
  @{
    fprintf(stderr, "\n prepare returned invalid field count");
    exit(0);
  @}

  /* Execute the SELECT query */
  if (mysql_execute(stmt))
  @{
    fprintf(stderr, "\n execute didn't retuned expected return code, MYSQL_NEED_DATA");
    exit(0);
  @}

  /* Bind the result data buffers */
  bzero(bind, 0, sizeof(bind));

  bind[0].buffer_type= MYSQL_TYPE_LONG;
  bind[0].buffer= (void *)&int_data;
  bind[0].length= &int_length;

  bind[1].buffer_type= MYSQL_TYPE_VAR_STRING;
  bind[1].buffer= (void *)str_data;
  bind[1].length= &str_length;

  if (mysql_bind_result(stmt, bind))
  @{
    fprintf(stderr, "\n bind_result failed");
    fprintf(stderr, "\n %s", mysql_stmt_error(stmt));
    exit(0);
  @}  

  /* Now fetch data to buffers */
  if (mysql_fetch(stmt))
  @{
    fprintf(stderr, "\n fetch failed");
    fprintf(stderr, "\n %s", mysql_stmt_error(stmt));
    exit(0);
  @}  
   
  fprintf(stdout, "\n int_data: %d, length: %ld", int_data, int_length);
  fprintf(stdout, "\n str_data: %s, length: %ld", str_data, str_length);
   
  /* call mysql_fetch again */
  if (mysql_fetch(stmt) |= MYSQL_NO_DATA)
  @{
    fprintf(stderr, "\n fetch return more than one row);
    exit(0);
  @}  

  /* Free the prepare result */
  mysql_free_result(result);

  /* Free the statement handle */
  if (mysql_stmt_free(stmt))
  @{
    fprintf(stderr, "\n failed to free the statement handle);
    fprintf(stderr, "\n %s", mysql_stmt_error(stmt));
    exit(0);
  @}  
 
@end example



@node mysql_send_long_data, mysql_stmt_close, mysql_fetch, C Prepared statement functions
@subsubsection @code{mysql_send_long_data()}


@findex @code{mysql_send_long_data()}.

@code{int mysql_send_long_data(MYSQL_STMT *stmt, unsigned int
parameter_number, const char *data, ulong length, my_bool is_last_data)}

@subsubheading Description

Allows an application to send the data in pieces or chunks to
server. This function can be used to send character or binary data
values in parts to a column(it must be a text or blob) with a character or
binary data type.

@sp 1
The @code{data} is a pointer to buffer containing the actual data for
the parameter represendted by @code{parameter_number}. The @code{length}
indicates the amount of data to be sent in bytes, and @code{is_last_data} is a
boolean flag to indicate the end of the data. If it is != 0, then the
current call will be the end of the data, else it waits for the
application to send all data. If the application doesn't ended the data
supply from @code{mysql_send_long_data()}, then the
@code{mysql_execute()} will return @strong{MYSQL_NEED_DATA}.



@subsubheading Return Values

Zero if the data is sent successfully to server. Non-zero if an error
occured.


@subsubheading Errors

@table @code
@item CR_INVALID_PARAMETER_NO
Invalid parameter number
@item CR_SERVER_GONE_ERROR
The MySQL server has gone away
@item CR_UNKNOWN_ERROR
An unkown error occured
@end table

@subsubheading Example
The following example explains how to send the data in chunks to text
column:
@example
  
MYSQL_BIND bind[1];
long       length;

  query= "INSERT INTO test_long_data(text_column) VALUES(?)");
  if (!mysql_prepare(&mysql, query, strlen(query))
  @{
    fprintf(stderr, "\n prepare failed");
    fprintf(stderr, "\n %s", mysql_error(&stmt));
    exit(0);
  @}
   memset(bind, 0, sizeof(bind));
   bind[0].buffer_type= MYSQL_TYPE_STRING;
   bind[0].length= &length;

   /* Indicate that the data supply is in CHUNKS */
   length= MYSQL_LONG_DATA;

  /* Bind the buffers */
  if (mysql_bind_param(stmt, bind))
  @{
    fprintf(stderr, "\n param bind failed");
    fprintf(stderr, "\n %s", mysql_stmt_error(stmt));
    exit(0);
  @}

  /* Execute the insert statement - It should return MYSQL_NEED_DATA */
  if (mysql_execute(stmt) != MYSQL_NEED_DATA)
  @{
    fprintf(stderr, "\n execute didn't retuned expected return code, MYSQL_NEED_DATA");
    exit(0);
  @}

   /* Supply data in chunks to server */
   if (!mysql_send_long_data(stmt,1,"MySQL",5,0))
  @{
    fprintf(stderr, "\n send_long_data failed");
    fprintf(stderr, "\n %s", mysql_stmt_error(stmt));
    exit(0);
  @}
   /* Supply the last piece of data */
   if (mysql_send_long_data(stmt,1," - The most popular open source database",40,1))
  @{
    fprintf(stderr, "\n send_long_data failed");
    fprintf(stderr, "\n %s", mysql_stmt_error(stmt));
    exit(0);
  @}

   /* Now, execute the query */
   if (mysql_execute(stmt))
  @{
    fprintf(stderr, "\n mysql_execute failed");
    fprintf(stderr, "\n %s", mysql_stmt_error(stmt));
    exit(0);
  @}

   This inserts the data, "MySQL - The most popular open source database" 
   to the field 'text_column'.  
@end example



@node mysql_stmt_close, mysql_stmt_errno, mysql_send_long_data, C Prepared statement functions
@subsubsection @code{mysql_stmt_close()}

@findex @code{mysql_stmt_close()}

@code{my_bool mysql_stmt_close(MYSQL_STMT *)}

@subsubheading Description

Closes the prepared statement. @code{mysql_stmt_close()} also
deallocates the statement handle pointed to by @code{stmt}.

@subsubheading Return Values

Zero if the statement was freed successfully. Non-zero if an error occured.


@subsubheading Errors

@table @code
@item CR_SERVER_GONE_ERROR
The MySQL server has gone away
@item CR_UNKNOWN_ERROR
An unkown error occured
@end table

@subsubheading Example

For the usage of @code{mysql_stmt_close()} refer to the Example from
@ref{mysql_execute,mysql_execute()}.



@node mysql_stmt_errno, mysql_stmt_error, mysql_stmt_close, C Prepared statement functions
@subsubsection @code{mysql_stmt_errno()}


@findex @code{mysql_stmt_errno()}

@code{unsigned int mysql_stmt_errno(MYSQL_STMT *stmt)}

@subsubheading Description

For the statement specified by @code{stmt}, @code{mysql_stmt_errno()}
returns the error code for the most recently invoked statement API
function that can succeed or fail. A return value of zero means that no
error occured. Client error message numbers are listed in the MySQL
errmsg.h header file. Server error message numbers are listed in
mysqld_error.h. In the MySQL source distribution you can find a complete
list of error messages and error numbers in the file Docs/mysqld_error.txt

@subsubheading Return Values

An error code value. Zero if no error occured.

@subsubheading Errors

None


@node mysql_stmt_error, mysql_commit, mysql_stmt_errno, C Prepared statement functions
@subsubsection @code{mysql_stmt_error()}


@findex @code{mysql_stmt_error()}.

@code{char *mysql_stmt_error(MYSQL_STMT *stmt)}

@subsubheading Description

For the statement specified by @code{stmt}, @code{mysql_stmt_error()}
returns the error message for the most recently invoked statement API
that can succeed or fail. An empty string ("") is returned if no error
occured. This means the following two sets are equivalent:

@example

if (mysql_stmt_errno(stmt))
@{
  // an error occured
@}

if (mysql_stmt_error(stmt))
@{
  // an error occured
@}
@end example

The language of the client error messages many be changed by recompiling
the MySQL client library. Currently you can choose error messages in
several different languages.


@subsubheading Return Values

A character string that describes the error. An empry string if no error
occured.

@subsubheading Errors

None



@node mysql_commit, mysql_rollback, mysql_stmt_error, C Prepared statement functions
@subsubsection @code{mysql_commit()}


@findex @code{mysql_commit()}.

@code{my_bool mysql_commit(MYSQL *mysql)}

@subsubheading Description

Commits the current transaction

@subsubheading Return Values

Zero if successful. Non-zero if an error occured.

@subsubheading Errors

None



@node mysql_rollback, mysql_autocommit, mysql_commit, C Prepared statement functions
@subsubsection @code{mysql_rollback()}


@findex @code{mysql_rollback()}.

@code{my_bool mysql_rollback(MYSQL *mysql)}

@subsubheading Description

Rollbacks the current transaction.


@subsubheading Return Values

Zero if successful. Non-zero if an error occured.

@subsubheading Errors

None.




@node mysql_autocommit,  , mysql_rollback, C Prepared statement functions
@subsubsection @code{mysql_autocommit()}


@findex @code{mysql_autocommit()}.

@code{my_bool mysql_autocommit(MYSQL *mysql, my_bool mode)}

@subsubheading Description

Sets the autocommit mode to on or off. If the @code{mode} is '1', then it
sets the autocommit mode to on, else to off in case of '0'.

@subsubheading Return Values

Zero if successful. Non-zero if an error occured

@subsubheading Errors

None.

@bye
