Information Schema KEY_COLUMN_USAGE Table
The Information Schema KEY_COLUMN_USAGE table shows which key columns have constraints.
It contains the following columns:
| Column | Description |
|---|---|
CONSTRAINT_CATALOG | Always def. |
CONSTRAINT_SCHEMA | Database name of the constraint. |
CONSTRAINT_NAME | Name of the constraint (PRIMARY for the primary key). |
TABLE_CATALOG | Always #def. |
TABLE_SCHEMA | Database name of the column constraint. |
TABLE_NAME | Table name of the column constraint. |
COLUMN_NAME | Column name of the constraint. |
ORDINAL_POSITION | Position of the column within the constraint. |
POSITION_IN_UNIQUE_CONSTRAINT | For foreign keys, the position in the unique constraint. |
REFERENCED_TABLE_SCHEMA | For foreign keys, the referenced database name. |
REFERENCED_TABLE_NAME | For foreign keys, the referenced table name. |
REFERENCED_COLUMN_NAME | For 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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