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MySQL 5.7 Reference Manual  /  ...  /  The Rewriter Query Rewrite Plugin

5.5.4 The Rewriter Query Rewrite Plugin

MySQL supports query rewrite plugins that can examine and possibly modify SQL statements received by the server before the server executes them. See Query Rewrite Plugins.

MySQL distributions include a postparse query rewrite plugin named Rewriter and scripts for installing the plugin and its associated elements. These elements work together to provide SELECT rewriting capability:

  • A server-side plugin named Rewriter examines SELECT statements and may rewrite them, based on its in-memory cache of rewrite rules. Standalone SELECT statements and SELECT statements in prepared statements are subject to rewriting. SELECT statements occurring within view definitions or stored programs are not subject to rewriting.

  • The Rewriter plugin uses a database named query_rewrite containing a table named rewrite_rules. The table provides persistent storage for the rules that the plugin uses to decide whether to rewrite statements. Users communicate with the plugin by modifying the set of rules stored in this table. The plugin communicates with users by setting the message column of table rows.

  • The query_rewrite database contains a stored procedure named flush_rewrite_rules() that loads the contents of the rules table into the plugin.

  • A loadable function named load_rewrite_rules() is used by the flush_rewrite_rules() stored procedure.

  • The Rewriter plugin exposes system variables that enable plugin configuration and status variables that provide runtime operational information.

The following sections describe how to install and use the Rewriter plugin, and provide reference information for its associated elements.