Question

我在字段timestamp中设置了一个包含许多错误条目的数据库（设置为0000-00-00 00:00:00，我想要做的是使用上一个有效时间戳更新此字段。我尝试过遗憾的是，这个查询没有成功（语法不被接受）：

UPDATE `scontrini` s1
SET s1.`timestamp` = 
    (SELECT TOP 1 s2.`timestamp`
        FROM `scontrini` s2
        WHERE s2.`timestamp` <> '0000-00-00 00:00:00' AND s2.`id` < s1.`id`
        ORDER BY s2.`id` DESC)
WHERE `scontrini`.`timestamp`= '0000-00-00 00:00:00';

有些解决方案建议使用inner join，但我没有测试某些值的相等性。

提前致谢。

修改

我按照建议将查询更改为：

UPDATE `scontrini` as s1
SET s1.`timestamp` = 
    (SELECT s2.`timestamp`
        FROM `scontrini` as  s2
        WHERE s2.`timestamp` <> '0000-00-00 00:00:00' AND s2.`id` < s1.`id`
        ORDER BY s2.`id` DESC LIMIT 1)
WHERE s1.`timestamp`= '0000-00-00 00:00:00';

但我仍然收到错误消息。

静态分析： 1.在SELECT附近：找到了一个新的陈述，但是这个陈述和前一个陈述之间没有分隔符。 2.接近第二WHERE：这种类型的条款已经过检验 3.接近第二WHERE：声明未被识别。

MySQL错误消息：

#1093 - Table 's1' is specified twice, both as a target for 'UPDATE' and as a separate source for data

谢谢。

Answer 1

TOP用于SQL服务器而不是MySQL。在子查询的末尾使用LIMIT来限制返回的行数。

UPDATE `scontrini` s1
SET s1.`timestamp` = 
    (SELECT s2.`timestamp`
        FROM `scontrini` s2
        WHERE s2.`timestamp` <> '0000-00-00 00:00:00' AND s2.`id` < s1.`id`
        ORDER BY s2.`id` DESC LIMIT 1)
WHERE `scontrini`.`timestamp`= '0000-00-00 00:00:00';

Answer 2

使用max（）和正确的日期格式

 UPDATE `scontrini` s1
 SET s1.`timestamp` = 
 (
    SELECT max(s2.`timestamp`)
    FROM `scontrini` s2
    WHERE  DATE_FORMAT(s2`timestamp`, '%Y-%m-%d %h:%i:%s') <> 
                    '0000-00-00 00:00:00' AND s2.`id`< s1.`id`
 )
WHERE  DATE_FORMAT(s1.`timestamp`, '%Y-%m-%d %h:%i:%s')= '0000-00-00 00:00:00';

Answer 3

尝试

UPDATE `scontrini` as s1
SET s1.`timestamp` = 
    (SELECT s2.`timestamp`
        FROM `scontrini` s2
        WHERE s2.`timestamp` <> '0000-00-00 00:00:00' AND s2.`id` < s1.`id`
        ORDER BY s2.`timestamp` DESC limit 0,1)
WHERE `s1`.`timestamp`= '0000-00-00 00:00:00';

MySQL嵌套更新

3 个答案: