您可以使用下面的设置操作：

before 
+--------+--------+
|id_post | itemID | 
+--------+--------+
|  1     |    hi1 |
|  3     |   hi3  |
|  27    |   hi27 |
|  45    |   hi45 |
|  67    |   hi67 |
|  69    |   hi69 |
+--------+--------+

after
--------------------

mysql> SET @nbr=0;
Query OK, 0 rows affected (0.00 sec)

mysql> update posts set id=@nbr:=@nbr+1 

+--------+--------+
|id_post | post   | 
+--------+--------+
|  1     |    hi1 |
|  2     |   hi3  |
|  3     |   hi27 |
|  4     |   hi45 |
|  5     |   hi67 |
|  6     |   hi69 |
+--------+--------+
6 rows in set (0.00 sec)

运行以下命令：

SET @x = 0;
ALTER TABLE `posts` AUTO_INCREMENT = 1;
UPDATE `posts` SET `id_post` = @x:= @x + 1;