How MySQL Deals with Constraints statement that you are using (Section 13.2.6, “INSERT Statement” , Section 13.2.13, “UPDATE Statement” , and so forth). You can get information about the number of rows actually inserted or updated with the  mysql_info()  C API function. You can also use the  SHOW WARNINGS  statement. See mysql_info(), and Section 13.7.7.42, “SHOW WARNINGS Statement” . InnoDB  and  NDB  tables support foreign keys. See Section 1.7.3.2, “FOREIGN KEY Constraints” . Foreign keys let you cross-reference related data across tables, and foreign key constraints help keep this spread-out data consistent. MySQL supports  ON UPDATE  and  ON DELETE  foreign key references in  CREATE TABLE  and  ALTER TABLE  statements. The available referential actions are  RESTRICT ,  CASCADE ,  SET NULL , and  NO ACTION  (the default). SET DEFAULT  is also supported by the MySQL Server but is currently rejected as invalid by  InnoDB . Since MySQL does not support deferred constraint checking,  NO ACTION  is treated as  RESTRICT . For the exact syntax supported by MySQL for foreign keys, see Section 13.1.20.5, “FOREIGN KEY Constraints” . MATCH FULL ,  MATCH PARTIAL , and  MATCH SIMPLE  are allowed, but their use should be avoided, as they cause the MySQL Server to ignore any  ON DELETE  or  ON UPDATE  clause used in the same statement.  MATCH  options do not have any other effect in MySQL, which in effect enforces  MATCH SIMPLE semantics full-time. MySQL requires that foreign key columns be indexed; if you create a table with a foreign key constraint but no index on a given column, an index is created. You can obtain information about foreign keys from the  INFORMATION_SCHEMA.KEY_COLUMN_USAGE table. An example of a query against this table is shown here: mysql>  SELECT TABLE_SCHEMA, TABLE_NAME, COLUMN_NAME, CONSTRAINT_NAME >  FROM INFORMATION_SCHEMA.KEY_COLUMN_USAGE >  WHERE REFERENCED_TABLE_SCHEMA IS NOT NULL; +--------------+---------------+-------------+-----------------+ | TABLE_SCHEMA | TABLE_NAME | COLUMN_NAME | CONSTRAINT_NAME | +--------------+---------------+-------------+-----------------+ | fk1 | myuser | myuser_id | f | | fk1 | product_order | customer_id | f2 | | fk1 | product_order | product_id | f1 | +--------------+---------------+-------------+-----------------+ 3 rows in set (0.01 sec) Information about foreign keys on  InnoDB  tables can also be found in the  INNODB_FOREIGN  and INNODB_FOREIGN_COLS  tables, in the  INFORMATION_SCHEMA  database. InnoDB  and  NDB  tables support foreign keys. By default, MySQL 8.0 rejects invalid or improper data values and aborts the statement in which they occur. It is possible to alter this behavior to be more forgiving of invalid values, such that the server coerces them to valid ones for data entry, by disabling strict SQL mode (see Section 5.1.11, “Server SQL Modes” ), but this is not recommended. Older versions of MySQL employed the forgiving behavior by default; for a description of this behavior, see Constraints on Invalid Data. 83 1.7.3.3 Enforced Constraints on Invalid Data 1.7.3.2 FOREIGN KEY Constraints