Question

I have the following table

id name address empid

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

I need to write a query to set empid starting from 1. How to write it please. Do i have to use a stored procedure to that or can do it with a normal query?

Thank You.

Answer 1

Here is a way to do it that utilizes a pretty obscure assignment operator in MySQL. This solution won’t skip numbers in the case of gaps in the primary key sequence like some of the other solutions.

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

Here is the proof:

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)