Manual:Site identifiers table

The site_identifiers table contains:

si_site
Id of site record in table.

si_type
One of two values:


 * interwiki: the key is an interwiki link identifier such as en, tr, simple
 * equivalent: the key is a navigation id used in e.g. the "language links" section

In most cases these entries are both present and are identical for Wikimedia sites. Some sites have only an interwiki entry, for example commons, mediawiki, meta.

si_key
A language code or other link code, such as en, tr, simple, commons, plwikimedia, identifying a site's type for purposes of links between sites in a wiki farm.

Schema summary
+-+--+--+-+-+---+ +-+--+--+-+-+---+ +-+--+--+-+-+---+
 * Field  | Type             | Null | Key | Default | Extra |
 * si_type | varbinary(32)   | NO   | PRI | NULL    |       |
 * si_key | varbinary(32)    | NO   | PRI | NULL    |       |
 * si_site | int(10) unsigned | NO  | MUL | NULL    |       |

+-+--+--+-+-+---+ +-+--+--+-+-+---+ +-+--+--+-+-+---+
 * Field  | Type             | Null | Key | Default | Extra |
 * si_site | int(10) unsigned | NO  | MUL | NULL    |       |
 * si_type | varbinary(32)   | NO   | PRI | NULL    |       |
 * si_key | varbinary(32)    | NO   | PRI | NULL    |       |

Indexes
 +--++--+--+-+---+-+--++--++-+---+ +--++--+--+-+---+-+--++--++-+---+ +--++--+--+-+---+-+--++--++-+---+
 * Table           | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
 * site_identifiers |         0 | PRIMARY  |            1 | si_type     | A         |           0 |     NULL | NULL   |      | BTREE      |         |               |
 * site_identifiers |         0 | PRIMARY  |            2 | si_key      | A         |           0 |     NULL | NULL   |      | BTREE      |         |               |
 * site_identifiers |         1 | si_site  |            1 | si_site     | A         |           0 |     NULL | NULL   |      | BTREE      |         |               |
 * site_identifiers |         1 | si_key   |            1 | si_key      | A         |           0 |     NULL | NULL   |      | BTREE      |         |               |