Question

我有下表：

--------------------------------------------------------------------------------
| id | pack_id | user_id |     start_date      |       end_date      | runtime |
--------------------------------------------------------------------------------
| 1  |    52   |   9     | 2019-04-09 11:53:00 | 2019-04-09 11:54:00 |   60    |
| 2  |    52   |   9     | 2019-04-09 11:58:00 |         NULL        |   NULL  |

我想更新同一end_date和runtime的最后一个ID的pack_id和user_id。 end_date必须采用当前日期时间。这是我的查询：

UPDATE 
    myTable 
SET 
    end_date = NOW(),
    runtime = TIMESTAMPDIFF(SECOND, start_date, NOW()) 
WHERE 
    id = (
        SELECT 
            max(id) 
        FROM 
            myTable 
        WHERE 
            user_id = '9' 
        AND 
            pack_id = '52'
    )

然后出现以下错误：

第1行的错误1093（HY000）：您无法指定目标表 “ myTable”用于FROM子句中的更新

Answer 1

您无法在MySQL中执行此操作，因此请使用JOIN：

UPDATE myTable t JOIN
       (SELECT max(id) as max_id
        FROM myTable 
        WHERE user_id = '9' AND pack_id = '52'
       ) tt
       ON t.id = tt.max_id
    SET t.end_date = NOW(),
        t.runtime = TIMESTAMPDIFF(SECOND, t.start_date, NOW()) ;

Answer 2

在子句中更深入地使用子查询

UPDATE 
    myTable 
SET 
    end_date = NOW(),
    runtime = TIMESTAMPDIFF(SECOND, start_date, NOW()) 
WHERE 
    id = (
 select id from (
        SELECT 
            max(id) as id
        FROM 
            myTable 
        WHERE 
            user_id = '9' 
        AND 
            pack_id = '52'
) a
    )

Answer 3

您需要一个子查询来创建一个临时值集，并避免在同一级别使用同一表进行更新和选择。您可以使用嵌套选择进行操作，例如：

UPDATE myTable 
SET  end_date = NOW(),
    runtime = TIMESTAMPDIFF(SECOND, start_date, NOW()) 
WHERE id = (
select  max_id from (
        SELECT 
            max(id)  max_id  
        FROM  myTable 
        WHERE  user_id = '9' 
        AND pack_id = '52'

        ) t   )

或子查询上的内部联接

UPDATE myTable m 
INNER JOIN (
        SELECT 
            max(id)  max_id  
        FROM  myTable 
        WHERE  user_id = '9' 
        AND pack_id = '52'

        ) t   ON t.max_id  =  m.id 

SET  end_date = NOW(),
    runtime = TIMESTAMPDIFF(SECOND, start_date, NOW())

使用子查询获取错误1093（HY000）

3 个答案: