MySQL主外键表关联表数据的同时删除

要求将满足某个条件的主表和相关联的几个子表的数据全部删除，其实这个要求很简单，如果子表在创建外键的时候指定了ON DELETE CA

条件：p（父表）没有ON DELETE CASCADE c（子表）

mysql> delete a,b from p a,c b where a.id=b.id;

ERROR 1451 (23000): Cannot delete or update a parent row: a foreign key constraint fails (`hhl`.`c`, CONSTRAINT `FK_P_ID` FOREIGN KEY (`id`) REFERENCES `p` (`id`))

mysql> show profiles ;

+----------+------------+------------------------------------------+

| Query_ID | Duration | Query |

+----------+------------+------------------------------------------+

| 1 | 0.00875600 | delete a,b from p a,c b where a.id=b.id |

| 2 | 0.01294200 | delete a,b from p a,c b where a.id=b.id |

+----------+------------+------------------------------------------+

mysql> show profile for query 2 ;

+--------------------------+----------+

| Status | Duration |

+--------------------------+----------+

| starting | 0.000314 |

| checking permissions | 0.000026 |

| checking permissions | 0.000014 |

| checking permissions | 0.000009 |

| checking permissions | 0.000010 |

| init | 0.000033 |

| Opening tables | 0.000082 |

| System lock | 0.000047 |

| init | 0.000050 |

| deleting from main table | 0.000016 |

| optimizing | 0.000019 |

| statistics | 0.000056 |

| preparing | 0.000042 |

| executing | 0.000054 |

| Sending data | 0.005026 |

| end | 0.000050 |

| query end | 0.003456 |

| closing tables | 0.000143 |

| freeing items | 0.003430 |

| logging slow query | 0.000047 |

| cleaning up | 0.000021 |

+--------------------------+----------+

21 rows in set (0.00 sec)

看出上面没有删除子表的操作。

mysql> delete a,b from c a,p b where a.id=b.id;

Query OK, 6 rows affected (0.04 sec)

from 后面 子表在前，，删除成功！！

mysql> show profile for query 3 ;

+--------------------------------+----------+

| Status | Duration |

+--------------------------------+----------+

| starting | 0.000307 |

| checking permissions | 0.000019 |

| checking permissions | 0.000017 |

| checking permissions | 0.000009 |

| checking permissions | 0.000010 |

| init | 0.000021 |

| Opening tables | 0.000091 |

| System lock | 0.000036 |

| init | 0.000047 |

| deleting from main table | 0.000016 |

| optimizing | 0.000125 |

| statistics | 0.000084 |

| preparing | 0.000042 |

| executing | 0.000013 |

| Sending data | 0.000572 |

| deleting from reference tables | 0.000103 |

| end | 0.000015 |

| Waiting for query cache lock | 0.000009 |

| end | 0.000010 |

| Waiting for query cache lock | 0.000008 |

| end | 0.000160 |

| end | 0.000022 |

| query end | 0.030033 |

| closing tables | 0.000081 |

| freeing items | 0.001465 |

| logging slow query | 0.000052 |

| cleaning up | 0.000011 |

+--------------------------------+----------+

27 rows in set (0.00 sec)

另一种方式： 先删除最外层的子表，一层一层向里删除，最后删除父表。

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