在我的数据库中,我有一个具有递归关联的表Employee
(员工可以是其他员工的老板):如何在MYSQL中删除相同的表?
create table if not exists `employee` (
`SSN` varchar(64) not null,
`name` varchar(64) default null,
`designation` varchar(128) not null,
`MSSN` varchar(64) default null,
primary key (`ssn`),
constraint `fk_manager_employee` foreign key (`mssn`) references employee(ssn)
) engine=innodb default charset=latin1;
mysql> describe Employee;
+-------------+--------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------------+--------------+------+-----+---------+-------+
| SSN | varchar(64) | NO | PRI | NULL | |
| name | varchar(64) | YES | | NULL | |
| designation | varchar(128) | NO | | NULL | |
| MSSN | varchar(64) | YES | MUL | NULL | |
+-------------+--------------+------+-----+---------+-------+
4 rows in set (0.00 sec)
然后插入:
mysql> insert into Employee values
-> ("1", "A", "OWNER", NULL),
-> ("2", "B", "BOSS", "1"),
-> ("3", "C", "WORKER", "2"),
-> ("4", "D", "BOSS", "2"),
-> ("5", "E", "WORKER", "4"),
-> ("6", "F", "WORKER", "1"),
-> ("7", "G", "WORKER", "4")
-> ;
Query OK, 7 rows affected (0.02 sec)
Records: 7 Duplicates: 0 Warnings: 0
现在我在表格中的行之间有以下等级关系(所有者>老板>工人):
A
/\
B F
/\
c D
/\
G E
以下是select语句表:
mysql> SELECT * FROM Employee;
+-----+------+-------------+------+
| SSN | name | designation | MSSN |
+-----+------+-------------+------+
| 1 | A | OWNER | NULL |
| 2 | B | BOSS | 1 |
| 3 | C | WORKER | 2 |
| 4 | D | BOSS | 2 |
| 5 | E | WORKER | 4 |
| 6 | F | WORKER | 1 |
| 7 | G | WORKER | 4 |
+-----+------+-------------+------+
7 rows in set (0.00 sec)
现在,我想强加约束,如:If any employee (BOSS) deleted then new BOSS of workers under him become immediate BOSS of deleted employee (Old BOSS)
。例如如果我删除D
,则B
成为G
和E
的BOSS。
为此,我也写了触发如下:
mysql> DELIMITER $$
mysql> CREATE
-> TRIGGER `Employee_before_delete` BEFORE DELETE
-> ON `Employee`
-> FOR EACH ROW BEGIN
-> UPDATE Employee
-> SET MSSN=old.MSSN
-> WHERE MSSN=old.MSSN;
-> END$$
Query OK, 0 rows affected (0.07 sec)
mysql> DELIMITER ;
但是当我执行一些缺失:
mysql> DELETE FROM Employee WHERE SSN='4';
ERROR 1442 (HY000): Can't update table 'Employee' in stored function/trigger
because it is already used by statement which invoked this stored
function/trigger.
我learn here是this trigger is not possible
因为In MySQL triggers can't manipulate the table they are assigned to
。
有没有一些其他可能的方式来做到这一点?它可能使用Nested Query
?有人能告诉我其他方法吗?一个建议就足够了,但应该是有效的。
编辑:
我得到了答案: INSTEAD OF触发器的stored procedure
或two consecutive queries
是可能的。 First和second。
我为此问题编写的解决方案如下,运行良好!:
- A作为我写
MYSQL version older then 5.5
一个辅助信号功能。
DELIMITER //
CREATE PROCEDURE `my_signal`(in_errortext VARCHAR(255)) BEGIN SET @sql=CONCAT('UPDATE `', in_errortext, '` SET x=1'); PREPARE my_signal_stmt FROM @sql; EXECUTE my_signal_stmt; DEALLOCATE PREPARE my_signal_stmt; END//
- 存储过程以从
Employee
表删除的雇员。
CREATE PROCEDURE delete_employee(IN dssn varchar(64)) BEGIN DECLARE empDesignation varchar(128); DECLARE empSsn varchar(64); DECLARE empMssn varchar(64); SELECT SSN, designation, MSSN INTO empSsn, empDesignation, empMssn FROM Employee WHERE SSN = dssn; IF (empSsn IS NOT NULL) THEN CASE WHEN empDesignation = 'OWNER' THEN CALL my_signal('Error: OWNER can not deleted!'); WHEN empDesignation = 'WORKER' THEN DELETE FROM Employee WHERE SSN = empSsn; WHEN empDesignation = 'BOSS' THEN BEGIN UPDATE Employee SET MSSN = empMssn WHERE MSSN = empSsn; DELETE FROM Employee WHERE SSN = empSsn; END; END CASE; ELSE CALL my_signal('Error: Not a valid row!'); END IF; END//
DELIMITER;
你可以尝试以下吗?它看起来对你的要求未免过于简单特意在具有动态删除的条款...... '更新Employee' '设置MSSN =(选择从employee' '其中SSN =“4” mssn);' 从雇员处删除ssn = 4;' – bonCodigo
@bonCodigo:你的意思是连续删除两个查询。可以考虑......但我必须考虑这个 - 谢谢! –
是两个连续的疑问。看起来,sql server中的EntityFramework提供了Repository Pattern - 它可以让你通过存储过程使存储库的删除函数递归。我本人没有亲自做过。也许你可以在这里模仿相同的东西。有趣的问题+1 – bonCodigo