在表的行中设置迭代值

Question

我有下表

id name address empid

1  AA   aa      0
2  BB   bb      0
3  CC   cc      0

我需要编写一个查询来设置empid从1开始.请如何编写它.我必须使用存储过程,还是可以使用普通查询？

谢谢.

Answer 1

这是一种利用MySQL中非常模糊的赋值运算符的方法.在主键序列中存在间隙的情况下,该解决方案不会像其他一些解决方案那样跳过数字.

set @count = 0;
update test set empid = @count := @count+1;

这是证明:

mysql> create table test (
    -> id int unsigned primary key auto_increment,
    -> name varchar(32) not null,
    -> address varchar(32) not null,
    -> empid int unsigned not null default 0
    -> ) engine=innodb;
Query OK, 0 rows affected (0.02 sec)

mysql> insert into test (name, address)
    -> values ('AA', 'aa'), ('BB', 'bb'), ('CC', 'cc');
Query OK, 3 rows affected (0.00 sec)
Records: 3  Duplicates: 0  Warnings: 0

mysql> select * from test;
+----+------+---------+-------+
| id | name | address | empid |
+----+------+---------+-------+
|  1 | AA   | aa      |     0 |
|  2 | BB   | bb      |     0 |
|  3 | CC   | cc      |     0 |
+----+------+---------+-------+
3 rows in set (0.00 sec)

mysql> set @count=0;
Query OK, 0 rows affected (0.00 sec)

mysql> update test set empid = @count := @count+1;
Query OK, 3 rows affected (0.00 sec)
Rows matched: 3  Changed: 3  Warnings: 0

mysql> select * from test;
+----+------+---------+-------+
| id | name | address | empid |
+----+------+---------+-------+
|  1 | AA   | aa      |     1 |
|  2 | BB   | bb      |     2 |
|  3 | CC   | cc      |     3 |
+----+------+---------+-------+
3 rows in set (0.00 sec)