Mega Code Archive
Using Foreign Keys
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In MySQL, InnoDB tables support checking of foreign key constraints.
For non-InnoDB tables, REFERENCES tbl_name(col_name) clause has no actual effect.
It serves only as a comment to the column.
mysql> CREATE TABLE person (
-> id SMALLINT UNSIGNED NOT NULL AUTO_INCREMENT,
-> name CHAR(60) NOT NULL,
-> PRIMARY KEY (id)
-> );
Query OK, 0 rows affected (0.03 sec)
mysql>
mysql> CREATE TABLE shirt (
-> id SMALLINT UNSIGNED NOT NULL AUTO_INCREMENT,
-> owner SMALLINT UNSIGNED NOT NULL REFERENCES person(id),
-> PRIMARY KEY (id)
-> );
Query OK, 0 rows affected (0.03 sec)
mysql>
mysql> desc person;
+-------+----------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------+----------------------+------+-----+---------+----------------+
| id | smallint(5) unsigned | NO | PRI | NULL | auto_increment |
| name | char(60) | NO | | | |
+-------+----------------------+------+-----+---------+----------------+
2 rows in set (0.00 sec)
mysql> desc shirt;
+-------+----------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------+----------------------+------+-----+---------+----------------+
| id | smallint(5) unsigned | NO | PRI | NULL | auto_increment |
| owner | smallint(5) unsigned | NO | | | |
+-------+----------------------+------+-----+---------+----------------+
2 rows in set (0.00 sec)
mysql>
mysql> drop table shirt;
Query OK, 0 rows affected (0.00 sec)
mysql> drop table person;
Query OK, 0 rows affected (0.02 sec)
mysql>
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