Questions

Questions and Answers

22.4.1: How do you manage stored routines?

It is always good practice to use a clear naming scheme for your stored routines. You can manage stored procedures with CREATE [FUNCTION|PROCEDURE], ALTER [FUNCTION|PROCEDURE], DROP [FUNCTION|PROCEDURE], and SHOW CREATE [FUNCTION|PROCEDURE]. You can obtain information about existing stored procedures using the ROUTINES table in the INFORMATION_SCHEMA database (see Section 19.14, “The INFORMATION_SCHEMA ROUTINES Table”).

22.4.2: Does MySQL 5.0 support stored procedures and functions?

Yes. MySQL 5.0 supports two types of stored routines — stored procedures and stored functions.

22.4.3: Can I print out a variable's value within a stored routine for debugging purposes?

Yes, you can do this in a stored procedure, but not in a stored function. If you perform an ordinary SELECT inside a stored procedure, the result set is returned directly to the client. You will need to use the MySQL 4.1 (or above) client-server protocol for this to work. This means that — for instance — in PHP, you need to use the mysqli extension rather than the old mysql extension.

22.4.4: Can a stored procedure call a trigger?

A stored procedure can execute an SQL statement, such as an UPDATE, that causes a trigger to activate.

22.4.5: Where can I find documentation for MySQL stored procedures and stored functions?

See Section 18.2, “Using Stored Routines (Procedures and Functions)”.

22.4.6: Can I return a cursor as an OUT parameter from a stored procedure?

In MySQL 5.0, cursors are available inside stored procedures only. However, if you do not open a cursor on a SELECT, the result will be sent directly to the client. You can also SELECT INTO variables. See Section 12.2.8, “SELECT Syntax”.

22.4.7: How are actions that take place inside stored procedures and functions replicated?

MySQL records each DML event that occurs in a stored procedure and replicates those individual actions to a slave server. The actual calls made to execute stored procedures are not replicated.

Stored functions that change data are logged as function invocations, not as the DML events that occur inside each function.

22.4.8: Is there a MySQL equivalent to using mod_plsql as a gateway on Apache to talk directly to a stored procedure in the database?

There is no equivalent in MySQL 5.0.

22.4.9: Is WITH RECOMPILE supported for stored procedures?

Not in MySQL 5.0.

22.4.10: Are there special security requirements for using stored procedures and functions together with replication?

Yes. Because a slave server has authority to execute any statement read from a master's binary log, special security constraints exist for using stored functions with replication. If replication or binary logging in general (for the purpose of point-in-time recovery) is active, then MySQL DBAs have two security options open to them:

22.4.11: What limitations exist for replicating stored procedure and function actions?

Nondeterministic (random) or time-based actions embedded in stored procedures may not replicate properly. By their very nature, randomly produced results are not predictable and cannot be exactly reproduced, and therefore, random actions replicated to a slave will not mirror those performed on a master. Note that declaring stored functions to be DETERMINISTIC or setting the log_bin_trust_function_creators system variable to 0 will not allow random-valued operations to be invoked.

In addition, time-based actions cannot be reproduced on a slave because the timing of such actions in a stored procedure is not reproducible through the binary log used for replication. It records only DML events and does not factor in timing constraints.

Finally, nontransactional tables for which errors occur during large DML actions (such as bulk inserts) may experience replication issues in that a master may be partially updated from DML activity, but no updates are done to the slave because of the errors that occurred. A workaround is for a function's DML actions to be carried out with the IGNORE keyword so that updates on the master that cause errors are ignored and updates that do not cause errors are replicated to the slave.

22.4.12: Is it possible to group stored procedures or stored functions into packages?

No. This is not supported in MySQL 5.0.

22.4.13: Can MySQL 5.0 stored routines return result sets?

Stored procedures can, but stored functions cannot. If you perform an ordinary SELECT inside a stored procedure, the result set is returned directly to the client. You need to use the MySQL 4.1 (or above) client-server protocol for this to work. This means that — for instance — in PHP, you need to use the mysqli extension rather than the old mysql extension.

22.4.14: Where can I find the ANSI SQL 2003 specification for stored procedures?

Unfortunately, the official specifications are not freely available (ANSI makes them available for purchase). However, there are books — such as SQL-99 Complete, Really by Peter Gulutzan and Trudy Pelzer — which give a comprehensive overview of the standard, including coverage of stored procedures.

22.4.15: What is being done to correct the aforementioned limitations?

MySQL 5.1 implements row-based replication, which resolves the limitations mentioned earlier.

We do not plan to backport row-based replication to MySQL 5.0. For additional information, see Replication Formats, in the MySQL 5.1 Manual.

22.4.16: Is there a way to view all stored procedures and stored functions in a given database?

Yes. For a database named dbname, use this query on the INFORMATION_SCHEMA.ROUTINES table:

SELECT ROUTINE_TYPE, ROUTINE_NAME
    FROM INFORMATION_SCHEMA.ROUTINES
    WHERE ROUTINE_SCHEMA='dbname';

For more information, see Section 19.14, “The INFORMATION_SCHEMA ROUTINES Table”.

The body of a stored routine can be viewed using SHOW CREATE FUNCTION (for a stored function) or SHOW CREATE PROCEDURE (for a stored procedure). See Section 12.4.5.8, “SHOW CREATE PROCEDURE Syntax”, for more information.

22.4.17: Do MySQL 5.0 stored procedures and functions work with replication?

Yes, standard actions carried out in stored procedures and functions are replicated from a master MySQL server to a slave server. There are a few limitations that are described in detail in Section 18.5, “Binary Logging of Stored Programs”.

22.4.18: Can I pass an array as input to a stored procedure?

Not in MySQL 5.0.

22.4.19: Can a stored procedure access tables?

Yes. A stored procedure can access one or more tables as required.

22.4.20: Are stored procedures and functions created on a master server replicated to a slave?

Yes, creation of stored procedures and functions carried out through normal DDL statements on a master server are replicated to a slave, so the objects will exist on both servers. ALTER and DROP statements for stored procedures and functions are also replicated.

22.4.21: Do stored procedures have a statement for raising application errors?

Not in MySQL 5.0. The SQL standard SIGNAL and RESIGNAL statements are implemented in MySQL 5.5.

22.4.22: Can I pass a cursor as an IN parameter to a stored procedure?

In MySQL 5.0, cursors are available inside stored procedures only.

22.4.23: Can a stored procedure call another stored procedure?

Yes.

22.4.24: Do the preceding limitations affect MySQL's ability to do point-in-time recovery?

The same limitations that affect replication do affect point-in-time recovery.

22.4.25: Is there a discussion forum for MySQL stored procedures?

Yes. See http://forums.mysql.com/list.php?98.

22.4.26: Do stored procedures provide exception handling?

MySQL implements HANDLER definitions according to the SQL standard. See Section 12.7.4.2, “DECLARE for Handlers”, for details.

22.4.27: Where are stored procedures stored?

In the proc table of the mysql system database. However, you should not access the tables in the system database directly. Instead, use SHOW CREATE FUNCTION to obtain information about stored functions, and SHOW CREATE PROCEDURE to obtain information about stored procedures. See Section 12.4.5.8, “SHOW CREATE PROCEDURE Syntax”, for more information about these statements.

You can also query the ROUTINES table in the INFORMATION_SCHEMA database — see Section 19.14, “The INFORMATION_SCHEMA ROUTINES Table”, for information about this table.

22.4.28: Can I commit or roll back transactions inside a stored procedure?

Yes. However, you cannot perform transactional operations within a stored function.