MYSQL - 如何更新由选择语句分组产生的所有项目的字段

MYSQL - how to update a field for all items resulting from group by select statement(MYSQL - 如何更新由选择语句分组产生的所有项目的字段)

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;

我想更新结果行的 field_flag.我如何在 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

您的意思是要更新 select 语句返回的集合中的 field1、field2 和 field3 的表吗?

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，更新可能会更新超过 1000 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

这样做的好处是可以稍后使用temptab，并且可以添加索引以加快更新:

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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