Question

我有一张像这样的表'虚拟'

name, status , date, is-updated
n1, s1, 2013-09-01, false
n2, s2, 2013-09-01, false
n1, s11, 2013-09-02, false

现在为了获取特定名称的最新时间戳，我正在使用查询：

select name, status, max(date)
from dummy
where is-updated=false
group by name,status

这正常工作正常，返回两行

n2, s2, 2013-09-01, false
n1, s11, 2013-09-02, false

现在如何将上面两行的'is-updated'值更新为'true'？ sql中的'IN'子句不支持多列。

update dummy
set is-updated = true
where name, status, date in (

select name, status, max(date)
from dummy
where is-updated=false
group by name,status

)

任何人都可以帮忙吗？感谢。

Answer 1

给我一些更多信息，我会更新这个更好：

update dummy as d 
     join ( 
       select name, max(modifieddate) as max_mod
       from dummy 
       where is_updated = FALSE 
       group by name ) as max_mod_tbl
      on max_mod_tbl.name = d.name and 
         max_mod_tbl.max_mod = d.modifieddate and 

set is_updated = true 

where d.is_updated = false

http://www.sqlfiddle.com/#!2/26bad/1/0

我添加了rows_you_want_to_change.is-updated = d.is-updated，因为...如果您有两行elect name, status, max(date) as dt和is-updated种状态

喜欢关键字段。并且该查询与您说它返回的行不匹配..？

Answer 2

您可以使用update和join执行此操作。正确的语法是：

update dummy join
       (select name, status, max(date) as maxdate
        from dummy
        where `is-updated` = false
        group by name, status
       ) toupdate
       on dummy.name = toupdate.name and
          dummy.status = toupdate.status and
          dummy.date = toupdate.maxdate
    set `is-updated` = true;

join执行过滤，因此您不需要where子句。

MAX上的基本SQL Update语句

2 个答案: