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C API Prepared Statement Function Overview

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If you obtained a

SELECT

statement's result set metadata by calling

mysql_stmt_result_metadata()

, you should also free the metadata using

mysql_free_result()

Execution Steps

To prepare and execute a statement, an application follows these steps:

1. Create a prepared statement handle with

mysql_stmt_init()

. To prepare the statement on the

server, call

mysql_stmt_prepare()

and pass it a string containing the SQL statement.

2. If the statement will produce a result set, call

mysql_stmt_result_metadata()

to obtain the

result set metadata. This metadata is itself in the form of result set, albeit a separate one from the
one that contains the rows returned by the query. The metadata result set indicates how many
columns are in the result and contains information about each column.

3. Set the values of any parameters using

mysql_stmt_bind_param()

. All parameters must be

set. Otherwise, statement execution returns an error or produces unexpected results.

4. Call

mysql_stmt_execute()

to execute the statement.

5. If the statement produces a result set, bind the data buffers to use for retrieving the row values by

calling

mysql_stmt_bind_result()

6. Fetch the data into the buffers row by row by calling

mysql_stmt_fetch()

repeatedly until no

more rows are found.

7. Repeat steps 3 through 6 as necessary, by changing the parameter values and re-executing the

statement.

When

mysql_stmt_prepare()

is called, the MySQL client/server protocol performs these actions:

• The server parses the statement and sends the okay status back to the client by assigning a

statement ID. It also sends total number of parameters, a column count, and its metadata if it is a
result set oriented statement. All syntax and semantics of the statement are checked by the server
during this call.

• The client uses this statement ID for the further operations, so that the server can identify the

statement from among its pool of statements.

When

mysql_stmt_execute()

is called, the MySQL client/server protocol performs these actions:

• The client uses the statement handle and sends the parameter data to the server.

• The server identifies the statement using the ID provided by the client, replaces the parameter

markers with the newly supplied data, and executes the statement. If the statement produces a result
set, the server sends the data back to the client. Otherwise, it sends an okay status and the number
of rows changed, deleted, or inserted.

When

mysql_stmt_fetch()

is called, the MySQL client/server protocol performs these actions:

• The client reads the data from the current row of the result set and places it into the application data

buffers by doing the necessary conversions. If the application buffer type is same as that of the field
type returned from the server, the conversions are straightforward.

Oracle 5.0, Reference Manual

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