Manual:Externallinks table

The externallinks table is where MediaWiki stores and tracks external links.

el_id
The primary key. Presently not used for anything, but will help with online schema changes.

el_from
The page>Special:MyLanguage/Manual:Page table#page_id|page id of the referring wiki page.

el_to
The actual URL itself. It is passed to the browser.

el_index
This is the same URL as  search-optimized: username and password information is stripped, and the other components are reversed for faster searching, so   becomes  , which allows searches of the form 'Show all links pointing to *.example.com'.

el_index_60
This is el_index truncated to 60 bytes to allow for sortable queries that aren't supported by a partial index.

Schema summary
+-+--+--+-+-++ +-+--+--+-+-++ +-+--+--+-+-++
 * Field      | Type             | Null | Key | Default | Extra          |
 * el_id      | int(10) unsigned | NO   | PRI | NULL    | auto_increment |
 * el_from    | int(10) unsigned | NO   | MUL | 0       |                |
 * el_to      | blob             | NO   | MUL | NULL    |                |
 * el_index   | blob             | NO   | MUL | NULL    |                |
 * el_index_60 | varbinary(60)   | NO   | MUL | NULL    |                |

+-+--+--+-+-++ +-+--+--+-+-++ +-+--+--+-+-++
 * Field      | Type             | Null | Key | Default | Extra          |
 * el_id      | int(10) unsigned | NO   | PRI | NULL    | auto_increment |
 * el_from    | int(10) unsigned | NO   | MUL | 0       |                |
 * el_to      | blob             | NO   | MUL | NULL    |                |
 * el_index   | blob             | NO   | MUL | NULL    |                |
 * el_index_60 | varbinary(60)   | NO   | MUL |         |                |

+--+--+--+-+-++ +--+--+--+-+-++ +--+--+--+-+-++
 * Field   | Type             | Null | Key | Default | Extra          |
 * el_id   | int(10) unsigned | NO   | PRI | NULL    | auto_increment |
 * el_from | int(10) unsigned | NO   | MUL | 0       |                |
 * el_to   | blob             | NO   | MUL | NULL    |                |
 * el_index | blob            | NO   | MUL | NULL    |                |

+--+--+--+-+-+---+ +--+--+--+-+-+---+ +--+--+--+-+-+---+
 * Field   | Type             | Null | Key | Default | Extra |
 * el_from | int(10) unsigned | NO   | MUL | 0       |       |
 * el_to   | blob             | NO   | MUL | NULL    |       |
 * el_index | blob            | NO   | MUL | NULL    |       |

+--+-+--+-+-+---+ +--+-+--+-+-+---+ +--+-+--+-+-+---+
 * Field   | Type            | Null | Key | Default | Extra |
 * el_from | int(8) unsigned | NO   | MUL | 0       |       |
 * el_to   | blob            | NO   | MUL | NULL    |       |
 * el_index | blob           | NO   | MUL | NULL    |       |