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MySQL 5.7 Reference Manual  /  ...  /  The View WITH CHECK OPTION Clause

22.5.4 The View WITH CHECK OPTION Clause

The WITH CHECK OPTION clause can be given for an updatable view to prevent inserts to rows for which the WHERE clause in the select_statement is not true. It aslo prevents updates to rows for which the WHERE clause is true but the update would cause it to be not true (in other words, it prevents visible rows from being updated to nonvisible rows).

In a WITH CHECK OPTION clause for an updatable view, the LOCAL and CASCADED keywords determine the scope of check testing when the view is defined in terms of another view. When neither keyword is given, the default is CASCADED.

Before MySQL 5.7.6, WITH CHECK OPTION testing works like this:

  • With LOCAL, the view WHERE clause is checked, but no underlying views are checked.

  • With CASCADED, the view WHERE clause is checked, then checking recurses to underlying views, adds WITH CASCADED CHECK OPTION to them (for purposes of the check; their definitions remain unchanged), and applies the same rules.

  • With no check option, the view WHERE clause is not checked, and no underlying views are checked.

As of MySQL 5.7.6, WITH CHECK OPTION testing is standard-compliant (with changed semantics from previously for LOCAL and no check clause):

  • With LOCAL, the view WHERE clause is checked, then checking recurses to underlying views and applies the same rules.

  • With CASCADED, the view WHERE clause is checked, then checking recurses to underlying views, adds WITH CASCADED CHECK OPTION to them (for purposes of the check; their definitions remain unchanged), and applies the same rules.

  • With no check option, the view WHERE clause is not checked, then checking recurses to underlying views, and applies the same rules.

Consider the definitions for the following table and set of views:

CREATE TABLE t1 (a INT);
CREATE VIEW v1 AS SELECT * FROM t1 WHERE a < 2
WITH CHECK OPTION;
CREATE VIEW v2 AS SELECT * FROM v1 WHERE a > 0
WITH LOCAL CHECK OPTION;
CREATE VIEW v3 AS SELECT * FROM v1 WHERE a > 0
WITH CASCADED CHECK OPTION;

Here the v2 and v3 views are defined in terms of another view, v1. Before MySQL 5.7.6, because v2 has a LOCAL check option, inserts are tested only against the v2 check. v3 has a CASCADED check option, so inserts are tested not only against the v3 check, but against those of underlying views. The following statements illustrate these differences:

mysql> INSERT INTO v2 VALUES (2);
Query OK, 1 row affected (0.00 sec)
mysql> INSERT INTO v3 VALUES (2);
ERROR 1369 (HY000): CHECK OPTION failed 'test.v3'

As of MySQL 5.7.6, the semantics for LOCAL differ from previously: Inserts for v2 are checked against its LOCAL check option, then (unlike before 5.7.6), the check recurses to v1 and the rules are applied again. The rules for v1 cause a check failure. The check for v3 fails as before:

mysql> INSERT INTO v2 VALUES (2);
ERROR 1369 (HY000): CHECK OPTION failed 'test.v2'
mysql> INSERT INTO v3 VALUES (2);
ERROR 1369 (HY000): CHECK OPTION failed 'test.v3'

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