information-schema-check-constraints.md

title	summary
CHECK_CONSTRAINTS	Learn the `CHECK_CONSTRAINTS` INFORMATION_SCHEMA table.

CHECK_CONSTRAINTS

The CHECK_CONSTRAINTS table provides information about CHECK constraints on tables.

USE INFORMATION_SCHEMA;
DESC CHECK_CONSTRAINTS;

The output is as follows:

+--------------------+-------------+------+-----+---------+-------+
| Field              | Type        | Null | Key | Default | Extra |
+--------------------+-------------+------+-----+---------+-------+
| CONSTRAINT_CATALOG | varchar(64) | NO   |     | NULL    |       |
| CONSTRAINT_SCHEMA  | varchar(64) | NO   |     | NULL    |       |
| CONSTRAINT_NAME    | varchar(64) | NO   |     | NULL    |       |
| CHECK_CLAUSE       | longtext    | NO   |     | NULL    |       |
+--------------------+-------------+------+-----+---------+-------+
4 rows in set (0.00 sec)

The following example adds a CHECK constraint using the CREATE TABLE statement:

SET GLOBAL tidb_enable_check_constraint = ON;
CREATE TABLE test.t1 (id INT PRIMARY KEY, CHECK (id%2 = 0));
SELECT * FROM CHECK_CONSTRAINTS\G

The output is as follows:

*************************** 1. row ***************************
CONSTRAINT_CATALOG: def
 CONSTRAINT_SCHEMA: test
   CONSTRAINT_NAME: t1_chk_1
      CHECK_CLAUSE: (`id` % 2 = 0)
1 row in set (0.00 sec)

Fields in the CHECK_CONSTRAINTS table are described as follows:

• CONSTRAINT_CATALOG: The catalog of the constraint, which is always def.
• CONSTRAINT_SCHEMA: The schema of the constraint.
• CONSTRAINT_NAME: The name of the constraint.
• CHECK_CLAUSE: The clause of the check constraint.