MYSQL-如何为group by select语句产生的所有项目更新字段 [英] MYSQL - how to update a field for all items resulting from group by select statement

问题描述

我有一个这样的选择:

SELECT field1, field2, field3 
FROM table WHERE field1= 5  AND field_flag =1 
GROUP BY field1, field2, field3 limit 1000;

我想为结果行更新field_flag.如何在MySQL中做到这一点?

I want to update field_flag for the resulting rows. How can I do that in MySQL?

推荐答案

是否表示要更新select语句返回的集合中field1，field2和field3所在的表?

Do you mean that you want to update table where field1, field2, and field3 are in the set returned by your select statement ?

例如

update table, 
     ( select field1, field2, field3 
       FROM table WHERE field1= 5  AND field_flag =1 
       GROUP BY field1, field2, field3 limit 1000 ) temp
set table.field_flag = 99 
where table.field1=temp.field1 and table.field2=temp.field2 and table.field3 = temp.field3

请注意，此更新可能会更新1000多个行.

Note that the update might update many more than 1000 rows.

也可以使用临时表:

create temporary table temptab as
select field1, field2, field3 
FROM table WHERE field1= 5  AND field_flag =1 
GROUP BY field1, field2, field3 limit 1000 

 update table, 
        temptab temp
 set table.field_flag = 99 
 where table.field1=temp.field1 and table.field2=temp.field2 and table.field3 = temp.field3

这具有以下优点:temptab可以在以后使用，还可以添加索引以加快更新速度:

This has the advantage that temptab can be used later, and also that indexes can be added to speed up the update:

create index on temptab (field1, field2, field3);

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