The Ultimate Guide to High Availability with MariaDB

Information Schema KEY_COLUMN_USAGE Table

The Information Schema KEY_COLUMN_USAGE table shows which key columns have constraints.

It contains the following columns:

ColumnDescription
CONSTRAINT_CATALOGAlways def.
CONSTRAINT_SCHEMADatabase name of the constraint.
CONSTRAINT_NAMEName of the constraint (PRIMARY for the primary key).
TABLE_CATALOGAlways #def.
TABLE_SCHEMADatabase name of the column constraint.
TABLE_NAMETable name of the column constraint.
COLUMN_NAMEColumn name of the constraint.
ORDINAL_POSITIONPosition of the column within the constraint.
POSITION_IN_UNIQUE_CONSTRAINTFor foreign keys, the position in the unique constraint.
REFERENCED_TABLE_SCHEMAFor foreign keys, the referenced database name.
REFERENCED_TABLE_NAMEFor foreign keys, the referenced table name.
REFERENCED_COLUMN_NAMEFor foreign keys, the referenced column name.

Example

SELECT * FROM information_schema.KEY_COLUMN_USAGE LIMIT 1 \G
********************** 1. row **********************
           CONSTRAINT_CATALOG: def
            CONSTRAINT_SCHEMA: my_website
              CONSTRAINT_NAME: PRIMARY
                TABLE_CATALOG: def
                 TABLE_SCHEMA: users
                  COLUMN_NAME: user_id
             ORDINAL_POSITION: 1
POSITION_IN_UNIQUE_CONSTRAINT: NULL
      REFERENCED_TABLE_SCHEMA: NULL
        REFERENCED_TABLE_NAME: NULL
       REFERENCED_COLUMN_NAME: NULL

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