Manual:categorylinks table

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MediaWiki database layout

categorylinks table

MediaWiki version:

≥ 1.3

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:

• The concatenation of cl_from and cl_to (for when an article is edited)
• The concatenation of cl_to, cl_type, cl_sortkey, and cl_from (for showing articles in order)
• The concatenation of cl_to and cl_timestamp
• cl_collation

Fields

cl_from

Stores the page.page_id of the article where the link was placed.

cl_to

Stores the name of the desired category in the page_title format (that is, with _ and excluding namespace prefix).

cl_sortkey

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_timestamp

Stores the time at which that link was last updated in the table.

cl_sortkey_prefix

This 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).

cl_collation

MediaWiki version:

≥ 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_type

What 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.

Schema summary

MediaWiki version:

≥ 1.17

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:

≥ 1.42

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      |         |               |
+---------------+------------+--------------+--------------+--------------+-----------+-------------+----------+--------+------+------------+---------+---------------+

See also

• API:Categorymembers

External links

• Example The page list of some category.