The categorylinks table stores entries corresponding to links of the form [[Category:Title]] or [[Category:Title|sortkey]], which when placed anywhere on a page places that page into the category named Title (for which an associated page may or may not exist). Links beginning with a colon, like [[:Category:Title]], are not stored in the categorylinks table, but are handled as normal internal links (in this case leading to the page Category:Title). The editable parts of category pages are stored like other pages.
There are four indexes which help improve performance:
cl_from and cl_to (for when an article is edited)cl_to, cl_type, cl_sortkey, and cl_from (for showing articles in order)cl_to and cl_timestampStores the page.page_id of the article where the link was placed.
cl_toStores the name of the desired category in the page_title format (that is, with _ and excluding namespace prefix).
Stores the title by which the page should be sorted in a category list. This is the binary sortkey, that depending on $wgCategoryCollation may or may not be readable by a human (but should sort in correct order when comparing as a byte string), and is not valid UTF-8 whenever the database truncates the sortkey in the middle of a multi-byte sequence.
cl_timestampStores the time at which that link was last updated in the table.
cl_sortkey_prefixThis is either the empty string if a page is using the default sortkey (aka the sortkey is unspecified). Otherwise it is the human readable version of the first part of cl_sortkey. Needed mostly so that cl_sortkey can be easily updated in certain situations without re-parsing the entire page. More recently added values are valid UTF-8 (see gerrit:449280).
≥ 1.17
What collation is in use. Used so that if the collation changes, the updateCollation.php script knows what rows need to be fixed in db.
cl_typeWhat type of page is this (file, subcat (subcategory) or page (normal page)). Used so that the different sections on a category page can be paged independently in an efficient manner.
Foreign key to collation.collation_id.
cl_target_idForeign key to linktarget.lt_id.
Schema summary MediaWiki version:≥ 1.44
DESCRIBE categorylinks;
+-------------------+------------------------------+------+-----+---------------------+-------------------------------+
| Field | Type | Null | Key | Default | Extra |
+-------------------+------------------------------+------+-----+---------------------+-------------------------------+
| cl_from | int(10) unsigned | NO | PRI | 0 | |
| cl_to | varbinary(255) | NO | PRI | | |
| cl_sortkey | varbinary(230) | NO | | | |
| cl_sortkey_prefix | varbinary(255) | NO | | | |
| cl_timestamp | timestamp | NO | | current_timestamp() | on update current_timestamp() |
| cl_collation | varbinary(32) | NO | | | |
| cl_type | enum('page','subcat','file') | NO | | page | |
| cl_collation_id | smallint(5) unsigned | NO | | 0 | |
| cl_target_id | bigint(20) unsigned | YES | MUL | NULL | |
+-------------------+------------------------------+------+-----+---------------------+-------------------------------+
MediaWiki versions:
1.17 – 1.43
DESCRIBE categorylinks;
+-------------------+------------------------------+------+-----+-------------------+-----------------------------+
| Field | Type | Null | Key | Default | Extra |
+-------------------+------------------------------+------+-----+-------------------+-----------------------------+
| cl_from | int(10) unsigned | NO | PRI | 0 | |
| cl_to | varbinary(255) | NO | PRI | | |
| cl_sortkey | varbinary(230) | NO | | | |
| cl_sortkey_prefix | varbinary(255) | NO | | | |
| cl_timestamp | timestamp | NO | | CURRENT_TIMESTAMP | on update CURRENT_TIMESTAMP |
| cl_collation | varbinary(32) | NO | MUL | | |
| cl_type | enum('page','subcat','file') | NO | | page | |
+-------------------+------------------------------+------+-----+-------------------+-----------------------------+
Warning: Starting with version 1.17, the index on (cl_to, cl_sortkey) is no more, and replaced with one on (cl_to, cl_type, cl_sortkey, cl_from). Extensions that directly query the categorylinks table to get a list of pages in sorted order need to make sure they are using the new index, or the query may become very inefficient MediaWiki versions:
1.10 – 1.16
DESCRIBE categorylinks;
+--------------+------------------+------+-----+-------------------+-----------------------------+ | Field | Type | Null | Key | Default | Extra | +--------------+------------------+------+-----+-------------------+-----------------------------+ | cl_from | int(10) unsigned | NO | PRI | 0 | | | cl_to | varbinary(255) | NO | PRI | | | | cl_sortkey | varbinary(70) | NO | | | | | cl_timestamp | timestamp | NO | | CURRENT_TIMESTAMP | on update CURRENT_TIMESTAMP | +--------------+------------------+------+-----+-------------------+-----------------------------+MediaWiki versions:
1.5 – 1.9
DESCRIBE categorylinks;
+--------------+-----------------+------+-----+-------------------+-----------------------------+ | Field | Type | Null | Key | Default | Extra | +--------------+-----------------+------+-----+-------------------+-----------------------------+ | cl_from | int(8) unsigned | NO | PRI | 0 | | | cl_to | varchar(255) | NO | PRI | | | | cl_sortkey | varchar(86) | NO | | | | | cl_timestamp | timestamp | NO | | CURRENT_TIMESTAMP | on update CURRENT_TIMESTAMP | +--------------+-----------------+------+-----+-------------------+-----------------------------+MediaWiki versions:
1.3 – 1.4
DESCRIBE categorylinks;
+--------------+-----------------+------+-----+-------------------+-----------------------------+ | Field | Type | Null | Key | Default | Extra | +--------------+-----------------+------+-----+-------------------+-----------------------------+ | cl_from | int(8) unsigned | NO | PRI | 0 | | | cl_to | varchar(255) | NO | PRI | | | | cl_sortkey | varchar(255) | NO | | | | | cl_timestamp | timestamp | NO | | CURRENT_TIMESTAMP | on update CURRENT_TIMESTAMP | +--------------+-----------------+------+-----+-------------------+-----------------------------+Indexes MediaWiki version:
≥ 1.44
SHOW INDEX IN categorylinks;
+---------------+------------+---------------+--------------+--------------+-----------+-------------+----------+--------+------+------------+---------+---------------+ | Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment | +---------------+------------+---------------+--------------+--------------+-----------+-------------+----------+--------+------+------------+---------+---------------+ | categorylinks | 0 | PRIMARY | 1 | cl_from | A | 0 | NULL | NULL | | BTREE | | | | categorylinks | 0 | PRIMARY | 2 | cl_to | A | 0 | NULL | NULL | | BTREE | | | | categorylinks | 1 | cl_sortkey | 1 | cl_to | A | 0 | NULL | NULL | | BTREE | | | | categorylinks | 1 | cl_sortkey | 2 | cl_type | A | 0 | NULL | NULL | | BTREE | | | | categorylinks | 1 | cl_sortkey | 3 | cl_sortkey | A | 0 | NULL | NULL | | BTREE | | | | categorylinks | 1 | cl_sortkey | 4 | cl_from | A | 0 | NULL | NULL | | BTREE | | | | categorylinks | 1 | cl_timestamp | 1 | cl_to | A | 0 | NULL | NULL | | BTREE | | | | categorylinks | 1 | cl_timestamp | 2 | cl_timestamp | A | 0 | NULL | NULL | | BTREE | | | | categorylinks | 1 | cl_sortkey_id | 1 | cl_target_id | A | 0 | NULL | NULL | YES | BTREE | | | | categorylinks | 1 | cl_sortkey_id | 2 | cl_type | A | 0 | NULL | NULL | | BTREE | | | | categorylinks | 1 | cl_sortkey_id | 3 | cl_sortkey | A | 0 | NULL | NULL | | BTREE | | | | categorylinks | 1 | cl_sortkey_id | 4 | cl_from | A | 0 | NULL | NULL | | BTREE | | | +---------------+------------+---------------+--------------+--------------+-----------+-------------+----------+--------+------+------------+---------+---------------+See also External links
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