title: REFERENTIAL_CONSTRAINTS summary: 了解 information_schema 表 REFERENTIAL_CONSTRAINTS。

REFERENTIAL_CONSTRAINTS

REFERENTIAL_CONSTRAINTS 表提供 TiDB 表之间 FOREIGN KEY 关系的信息。请注意，目前 TiDB 不强制进行 FOREIGN KEY 约束，也不执行 ON DELETE CASCADE 等操作。

USE information_schema;
DESC referential_constraints;

+---------------------------+--------------+------+------+---------+-------+
| Field                     | Type         | Null | Key  | Default | Extra |
+---------------------------+--------------+------+------+---------+-------+
| CONSTRAINT_CATALOG        | varchar(512) | NO   |      | NULL    |       |
| CONSTRAINT_SCHEMA         | varchar(64)  | NO   |      | NULL    |       |
| CONSTRAINT_NAME           | varchar(64)  | NO   |      | NULL    |       |
| UNIQUE_CONSTRAINT_CATALOG | varchar(512) | NO   |      | NULL    |       |
| UNIQUE_CONSTRAINT_SCHEMA  | varchar(64)  | NO   |      | NULL    |       |
| UNIQUE_CONSTRAINT_NAME    | varchar(64)  | YES  |      | NULL    |       |
| MATCH_OPTION              | varchar(64)  | NO   |      | NULL    |       |
| UPDATE_RULE               | varchar(64)  | NO   |      | NULL    |       |
| DELETE_RULE               | varchar(64)  | NO   |      | NULL    |       |
| TABLE_NAME                | varchar(64)  | NO   |      | NULL    |       |
| REFERENCED_TABLE_NAME     | varchar(64)  | NO   |      | NULL    |       |
+---------------------------+--------------+------+------+---------+-------+
11 rows in set (0.00 sec)

CREATE TABLE test.parent (
 id INT NOT NULL AUTO_INCREMENT,
 PRIMARY KEY (id)
);
CREATE TABLE test.child (
 id INT NOT NULL AUTO_INCREMENT,
 name varchar(255) NOT NULL,
 parent_id INT DEFAULT NULL,
 PRIMARY KEY (id),
 CONSTRAINT fk_parent FOREIGN KEY (parent_id) REFERENCES parent (id) ON UPDATE CASCADE ON DELETE RESTRICT
);
SELECT * FROM referential_constraints\G

*************************** 1. row ***************************
       CONSTRAINT_CATALOG: def
        CONSTRAINT_SCHEMA: test
          CONSTRAINT_NAME: fk_parent
UNIQUE_CONSTRAINT_CATALOG: def
 UNIQUE_CONSTRAINT_SCHEMA: test
   UNIQUE_CONSTRAINT_NAME: PRIMARY
             MATCH_OPTION: NONE
              UPDATE_RULE: CASCADE
              DELETE_RULE: RESTRICT
               TABLE_NAME: child
    REFERENCED_TABLE_NAME: parent
1 row in set (0.00 sec)