> For the complete documentation index, see [llms.txt](https://docs.postgresql.tw/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.postgresql.tw/12/client-interfaces/the-information-schema/constraint_column_usage.md).

# 36.18. constraint\_column\_usage

The view `constraint_column_usage` identifies all columns in the current database that are used by some constraint. Only those columns are shown that are contained in a table owned by a currently enabled role. For a check constraint, this view identifies the columns that are used in the check expression. For a foreign key constraint, this view identifies the columns that the foreign key references. For a unique or primary key constraint, this view identifies the constrained columns.

## **Table 36.16. `constraint_column_usage` Columns**

| Name                 | Data Type        | Description                                                                                                                         |
| -------------------- | ---------------- | ----------------------------------------------------------------------------------------------------------------------------------- |
| `table_catalog`      | `sql_identifier` | Name of the database that contains the table that contains the column that is used by some constraint (always the current database) |
| `table_schema`       | `sql_identifier` | Name of the schema that contains the table that contains the column that is used by some constraint                                 |
| `table_name`         | `sql_identifier` | Name of the table that contains the column that is used by some constraint                                                          |
| `column_name`        | `sql_identifier` | Name of the column that is used by some constraint                                                                                  |
| `constraint_catalog` | `sql_identifier` | Name of the database that contains the constraint (always the current database)                                                     |
| `constraint_schema`  | `sql_identifier` | Name of the schema that contains the constraint                                                                                     |
| `constraint_name`    | `sql_identifier` | Name of the constraint                                                                                                              |


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