Question

我在从联接更新表时遇到问题。我做了很多次这样的更新，但现在它不起作用。这是原始查询：

select 
surveydatakey
,a.Strata as [surveydata strata]
,SurveyPeriod
,DateOfSurvey
,StationLocation 
,a.CardType
,a.timeperiod
,station_entrance
,Direction
,DayType
,EntranceType
,b.Strata as ActuaStrata 
,StartDate
,currentdate
from surveydata a
inner join MAP_Entrance_Population b
on a.station_entrance_id = b.station_entrance_id
and a.timeperiod = b.tp
and  a.strata <> b.strata
where mode = 'train'
and a.strata not in (1,14,15,21,22,23)
and dateofsurvey between startdate and  currentdate
order by a.strata

现在这是更新查询：

begin tran
update a
set a.strata = b.strata
from surveydata a
inner join MAP_Entrance_Population b
on a.station_entrance_id = b.station_entrance_id
and a.timeperiod = b.tp
and  a.strata <> b.strata
where mode = 'train'
and a.strata not in (1,14,15,21,22,23)
and dateofsurvey between startdate and currentdate

搜索查询生成218个结果，更新说它会更改218个结果。在我的搜索查询中，我的条件是a.strata＆lt;＆gt; b.strata。我的目标是让这两个人相等。所以我想在我的更新查询后，我不应该在我的选择查询中得到任何结果。但实际上并没有改变。在进行更新后，我仍然得到相同的218个结果。

有什么想法吗？

Answer 1

是否可以，因为表B中没有任何记录根据您的连接条件加入表A？

尝试运行以下查询

select *
 from surveydata a
where mode = 'train'
and a.strata not in (1,14,15,21,22,23)
and dateofsurvey between startdate and currentdate 
and not exists
(
     SELECT 1
from MAP_Entrance_Population b
WHERE a.station_entrance_id = b.station_entrance_id
and a.timeperiod = b.tp
and  a.strata <> b.strata
 )

Answer 2

尝试以下两个查询

select 
.
.
.
from surveydata a
inner join MAP_Entrance_Population b
on a.station_entrance_id = b.station_entrance_id
and a.timeperiod = b.tp
where a.strata <> b.strata
and mode = 'train'
and a.strata not in (1,14,15,21,22,23)
and dateofsurvey between startdate and  currentdate
order by a.strata

更新

update a
set a.strata = b.strata
from surveydata a
inner join MAP_Entrance_Population b
on a.station_entrance_id = b.station_entrance_id
and a.timeperiod = b.tp
where a.strata <> b.strata
and mode = 'train'
and a.strata not in (1,14,15,21,22,23)
and dateofsurvey between startdate and currentdate

Answer 3

如果MAP_Entrance_Population中的218条记录strata设置为NULL，则您所描述的内容可能会发生。在这种情况下，您的选择查询会将行恢复为NULL is not equal to NULL或其他任何内容，并且您的更新查询将更新surveydata以将strata设置为NULL，这是仍然不等于NULL。

当您发现令人惊讶的事情时，您无法理解SQL中的比较运算符，通常根本原因是您将某些内容与NULL进行比较。

SQL不从连接更新

3 个答案: