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19.2. Stored Procedure Syntax

A stored routine is either a procedure or a function. Stored routines are created with CREATE PROCEDURE and CREATE FUNCTION statements. A procedure is invoked using a CALL statement, and can only pass back values using output variables. A function can be called from inside a statement just like any other function (that is, by invoking the function's name), and can return a scalar value. Stored routines may call other stored routines.

A stored procedure or function is associated with a particular database. This has several implications:

  • When the routine is invoked, an implicit USE db_name is performed (and undone when the routine terminates). USE statements within stored routines are disallowed.

  • You can qualify routine names with the database name. This can be used to refer to a routine that is not in the current database. For example, to invoke a stored procedure p or function f that is associated with the test database, you can say CALL test.p() or test.f().

  • When a database is dropped, all stored routines associated with it are dropped as well.

MySQL supports the very useful extension that allows the use of regular SELECT statements (that is, without using cursors or local variables) inside a stored procedure. The result set of such a query is simply sent directly to the client. Multiple SELECT statements generate multiple result sets, so the client must use a MySQL client library that supports multiple result sets. This means the client must use a client library from a version of MySQL at least as recent as 4.1. The client should also specify the CLIENT_MULTI_STATEMENTS option when it connects. For C programs, this can be done with the mysql_real_connect() C API function (see Section 25.2.3.51, “mysql_real_connect()).

The following sections describe the syntax used to create, alter, drop, and invoke stored procedures and functions.


 
 
  Published under the terms of the GNU General Public License Design by Interspire