Manual:Coding conventions/Database

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This page describes the coding conventions used within files of the MediaWiki codebase written for usage with a Database. See also the general conventions that apply to all program languages, including those for databases. If you would like a short checklist to help you review your commits, try using the Pre-commit checklist .


Use UPPERCASE for MySQL/MariaDB keywords, and lowercase for things like types. Do not specify the lengths of numeric types, but do for varchar() and varbinary() types. Use varbinary(14) for all timestamps, and parse them to the standard format using $dbw->timestamp( $ts ); do not use the timestamp field type.

Make sure to include the /*_*/ comment immediately before any table name; this will be replaced with the wiki's database prefix if necessary, and omitting it will cause breakage. Similarly, include the /*$wgDBTableOptions*/ comment after any table declaration, and /*i*/ immediately before any index names.

Create indexes as separate statements, do not include them in the table creation query; the separate syntax is clearer and makes it easier to see the difference between unique and non-unique indexes. Don't create indexes with ALTER TABLE ... ADD INDEX ..., always use CREATE INDEX ... ON ... instead.

-- Track page-to-page hyperlinks within the wiki.
CREATE TABLE /*_*/pagelinks (
  -- Key to the page_id of the page containing the link.
  pl_from int unsigned NOT NULL default 0,

  -- Key to page_namespace/page_title of the target page.
  -- The target page may or may not exist, and due to renames
  -- and deletions may refer to different page records as time
  -- goes by.
  pl_namespace int NOT NULL default 0,
  pl_title varchar(255) binary NOT NULL default ''
) /*$wgDBTableOptions*/;

CREATE UNIQUE INDEX /*i*/pl_from ON /*_*/pagelinks (pl_from,pl_namespace,pl_title);
CREATE UNIQUE INDEX /*i*/pl_namespace ON /*_*/pagelinks (pl_namespace,pl_title,pl_from);

All new tables should have a PRIMARY KEY, preferably a single AUTO_INCREMENT ID.


SQLite uses the same SQL as MySQL/MariaDB, so the SQL must be compatible with both. Usually, this can be accomplished with a few simple rules, given at Manual:Database access#SQLite compatibility.

Table namingEdit

  • Table names should be singular nouns: user, page, revision, etc. There are some historical exceptions: pagelinks, categorylinks
  • Column names are given a prefix derived from the table name: the name itself if it's short, or an abbreviation:
    • pagepage_id, page_namespace, page_title
    • categorylinkscl_from, cl_namespace

Changing the schemaEdit

See Development policy#Database_patches, especially Special:Diff/537762/prev.

When updating the schema for an extension, it is advisable to both update the original schema file and create a patch file for those updating from a previous version.