mysql>
mysql> CREATE TABLE T1
-> (A INTEGER NOT NULL PRIMARY KEY,
-> B INTEGER NOT NULL);
Query OK, 0 rows affected (0.00 sec)
mysql>
mysql>
mysql> CREATE TABLE T2
-> (A INTEGER NOT NULL PRIMARY KEY,
-> B INTEGER NOT NULL,
-> CONSTRAINT C1 CHECK (B > 0),
-> CONSTRAINT FK1 FOREIGN KEY (A) REFERENCES T1 (A));
Query OK, 0 rows affected (0.00 sec)
mysql>
mysql> ALTER TABLE T1
-> ADD CONSTRAINT FK2 FOREIGN KEY (A) REFERENCES T2 (A);
Query OK, 0 rows affected (0.01 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql>
mysql>
mysql> drop table t1;
ERROR 1217 (23000): Cannot delete or update a parent row: a foreign key constraint fails
mysql> drop table t2;
ERROR 1217 (23000): Cannot delete or update a parent row: a foreign key constraint fails