Question

我有一个看起来像这样的表：

entity_guid    | name           | value
---------------|----------------|--------
189501         | context        | groups
189501         | column         | 3
189509         | context        | profile
189509         | column         | 3
189521         | context        | profile
189521         | column         | 2
189551         | context        | groups
189551         | column         | 1
189552         | context        | groups
189552         | column         | 3
189554         | context        | groups
189554         | column         | 2
189559         | context        | profile
189559         | column         | 1
189591         | context        | profile
189591         | column         | 3

我想要更新name = column和value = 3的行，以便value = 2。但我只想更新另一行存在的行entity_guid以及name = context和value = groups。

例如，如果我要选择要更改的行，它们将是：

entity_guid    | name           | value
---------------|----------------|--------
189501         | column         | 3
189552         | column         | 3

我试过了：

SELECT * FROM (
    SELECT * FROM `elggprivate_settings` WHERE `name` = 'context' AND `value` = 'groups'
) AS subquery
WHERE `name` = 'column' AND `value` = 3

但那当然不起作用，因为表没有像那样设置;同一entity_guid有多行。顺便说一下，这是社交网络引擎elgg的数据库中的表。我对MySQL不是很好，也无法在线找到答案。

Answer 1

xQbert很接近，但他忘记了用于检查子记录存在的context / groups子句。

UPDATE 
  elggprivate_settings
SET
   value = '2'
WHERE
   name = 'column' AND value = '3'
   AND entity_guid IN (
     SELECT 
       entity_guid 
     FROM 
       elggprivate_settings 
     WHERE 
       name = 'context'  
       AND value = 'groups')

Answer 2

最快的方法是将表连接到自身（连接通常比子查询更快）：

UPDATE elggprivate_settings es
 JOIN elggprivate_settings es2
   ON es2.entity_guid = es.entity_guid
SET es.value = '2'
WHERE es.value = '3'
AND es.name = 'column'
AND es2.name = 'context'
and es2.value = 'groups';

MySQL子查询基于其他行

2 个答案: