|
| 1 | +--- |
| 2 | +title: CHECK_CONSTRAINTS |
| 3 | +summary: Learn the `CHECK_CONSTRAINTS` INFORMATION_SCHEMA table. |
| 4 | +--- |
| 5 | + |
| 6 | +# CHECK\_CONSTRAINTS |
| 7 | + |
| 8 | +The `CHECK_CONSTRAINTS` table provides information about [`CHECK` constraints](/constraints.md#check) on tables. |
| 9 | + |
| 10 | +```sql |
| 11 | +USE INFORMATION_SCHEMA; |
| 12 | +DESC CHECK_CONSTRAINTS; |
| 13 | +``` |
| 14 | + |
| 15 | +The output is as follows: |
| 16 | + |
| 17 | +```sql |
| 18 | ++--------------------+-------------+------+-----+---------+-------+ |
| 19 | +| Field | Type | Null | Key | Default | Extra | |
| 20 | ++--------------------+-------------+------+-----+---------+-------+ |
| 21 | +| CONSTRAINT_CATALOG | varchar(64) | NO | | NULL | | |
| 22 | +| CONSTRAINT_SCHEMA | varchar(64) | NO | | NULL | | |
| 23 | +| CONSTRAINT_NAME | varchar(64) | NO | | NULL | | |
| 24 | +| CHECK_CLAUSE | longtext | NO | | NULL | | |
| 25 | ++--------------------+-------------+------+-----+---------+-------+ |
| 26 | +4 rows in set (0.00 sec) |
| 27 | +``` |
| 28 | + |
| 29 | +The following example adds a `CHECK` constraint using the `CREATE TABLE` statement: |
| 30 | + |
| 31 | +```sql |
| 32 | +CREATE TABLE test.t1 (id INT PRIMARY KEY, CHECK (id%2 = 0)); |
| 33 | +SELECT * FROM CHECK_CONSTRAINTS\G |
| 34 | +``` |
| 35 | + |
| 36 | +The output is as follows: |
| 37 | + |
| 38 | +```sql |
| 39 | +*************************** 1. row *************************** |
| 40 | +CONSTRAINT_CATALOG: def |
| 41 | + CONSTRAINT_SCHEMA: test |
| 42 | + CONSTRAINT_NAME: t1_chk_1 |
| 43 | + CHECK_CLAUSE: (`id` % 2 = 0) |
| 44 | +1 row in set (0.00 sec) |
| 45 | +``` |
| 46 | + |
| 47 | +Fields in the `CHECK_CONSTRAINTS` table are described as follows: |
| 48 | + |
| 49 | +* `CONSTRAINT_CATALOG`: The catalog of the constraint, which is always `def`. |
| 50 | +* `CONSTRAINT_SCHEMA`: The schema of the constraint. |
| 51 | +* `CONSTRAINT_NAME`: The name of the constraint. |
| 52 | +* `CHECK_CLAUSE`: The clause of the check constraint. |
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