Question

我在sql中有这个查询： -

Select
    * 
from
    ClassNote C 
    Join ClassSubMatRelation CSMR on C.ClassNoteID=CSMR.ClassNoteFK 
where
    CSMR.BoardFK = 1 
    and
    CSMR.SubjectFK in
        (
            select
                t.SubjectFK
            from
                ClassSubMatRelation t
            where
                t.BoardFK = 1
        ) 
    and
    CSMR.SubjectFK not in
        (
           select
                e.SubjectFK
            from
                ClassSubMatRelation e
            where
                e.BoardFK != 1
        ) 
    and
    CSMR.Status_Info = 1
    and
    CSMR.ClassNoteFK is not null

查询工作正常。但我想我可以使用连接来使其更简单，更快捷。如你所见，我是新手，所以无法弄清楚我该怎么做。我尝试了其他解决方案，但是他们没有正常工作。

我的表架构： -

ClassNote (
    ClassNoteID
    Heading
    ClassNoteDesc
    ClassNoteRefID
    Status_Info
)

ClassSubMatRelation (
    ClassSubMatRelationID
    BoardFK
    ClassFK
    SubjectFK
    MaterialFK
    ClassNoteFK
    ClassEbookFK
    ClassSPFK
    Status_Info
)

Answer 1

您可以通过将部分WHERE移至JOIN的{{1}}语句，对加入CSMR设置一些限制。像这样：

ON

但我不认为这会加快速度。 SQL Server非常好地优化......至少它阅读起来有点简单。

编辑 - 现在我看一下，这两个IN声明是否必要？ IN正在获得所有BoardFK = 1并且NOT IN确保你得到的不是1 ...... 既然你已经在那里明确指定BoardFK = 1，你就不需要那些......所以，像这样：

Select * 
from ClassNote C 
Join ClassSubMatRelation CSMR 
  on C.ClassNoteID=CSMR.ClassNoteFK
  and CSMR.Status_Info=1 
  and CSMR.ClassNoteFK is not null
  and CSMR.BoardFK = 1

where CSMR.SubjectFK in (select t.SubjectFK from ClassSubMatRelation t where t.BoardFK=1) 
and CSMR.SubjectFK not in (select e.SubjectFK from ClassSubMatRelation e where e.BoardFK!=1)

注意：如果您决定将其更改为OUTER JOIN，那么这样做将不会表现相同。

Answer 2

你可以尝试一下

Select
    * 
from
    ClassNote C 
    Join ClassSubMatRelation CSMR on C.ClassNoteID=CSMR.ClassNoteFK AND 
        CSMR.BoardFK = 1  
    AND 
        CSMR.Status_Info = 1
    AND  
        CSMR.ClassNoteFK is not null
    Join ClassSubMatRelation t on t.SubjectFK = CSMR.SubjectFK AND t.BoardFK = 1
    LEFT JOIN ClassSubMatRelation e ON e.SubjectFK AND e.BoardFK != 1 AND e.SubjectFK IS NULL

Answer 3

我注意到你的第二个CSMR.SubjectFK子句是多余的：第一个只匹配t.BoardFK = 1的行，而第二个子句排除t.BoardFK != 1的行，但它们已被排除在外第一个条款，使它完全是多余的。它们都可以替换为单个INNER JOIN：

SELECT
    ClassNote.*
FROM
    ClassNote
    INNER JOIN ClassSubMatRelation AS csmr ON ClassNote.ClassNoteId = csmr.ClassNoteFK
    LEFT OUTER JOIN ClassSubMatRelation AS subject ON csmr.SubjectFK = subject.SubjectFK
WHERE
    csmr.BoardFK = 1
    AND
    subject.SubjectFK = 1
    AND
    csmr.Status_Info = 1

在Sql查询中使用Join

3 个答案: