Sql 将多个表中的值作为一个resultset中的字段返回

我有以下查询，它返回一组结果，其中填充了另一个表中的值：

select  mjc,
    name,
    (SELECT TOP 1 pageID FROM page WHERE mjc = 'ABC' ORDER BY createdOn DESC) AS LastCreatedId,
    (SELECT TOP 1 pageName FROM page WHERE mjc = 'ABC' ORDER BY createdOn DESC) AS LastCreatedName,
    (SELECT TOP 1 createdOn FROM page WHERE mjc = 'ABC' ORDER BY createdOn DESC) AS LastCreatedDate,
    (SELECT TOP 1 pageID FROM page WHERE mjc = 'ABC' ORDER BY modifiedOn DESC) AS LastEditedId,
    (SELECT TOP 1 pageName FROM page WHERE mjc = 'ABC' ORDER BY modifiedOn DESC) AS LastEditedName,
    (SELECT TOP 1 modifiedOn FROM page WHERE mjc = 'ABC' ORDER BY modifiedOn DESC) AS LastEditedDate,
    (SELECT COUNT(*) FROM page WHERE mjc = 'ABC' AND published = 1) AS PublishedPages,
    (SELECT COUNT(*) FROM page WHERE mjc = 'ABC' AND published = 0) AS UnpublishedPages
from mags
WHERE mjc IN ('ABC')

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我只是想知道是否有一种更有效的方法来实现这一点，例如使用连接？

您可以在一定程度上优化子查询。这些预测如下：

(SELECT TOP 1 pageID FROM page WHERE mjc = 'ABC' ORDER BY createdOn DESC),
(SELECT TOP 1 pageName FROM page WHERE mjc = 'ABC' ORDER BY createdOn DESC),
(SELECT TOP 1 createdOn FROM page WHERE mjc = 'ABC' ORDER BY createdOn DESC),

也可以这样重新编写：

SELECT t.pageID AS LastCreatedId, 
       t.pageName AS LastCreatedName, 
       t.createdOn AS LastCreatedDate
FROM (SELECT TOP 1 pageID, pageName, createdOn
      FROM page where mjc = 'ABC' ORDER BY createdOn DESC) t

或者在更大的背景下

SELECT
    mjc,
    name,
    t.pageID AS LastCreatedId, 
    t.pageName AS LastCreatedName, 
    t.createdOn AS LastCreatedDate
FROM mags,
    (SELECT TOP 1 pageID, pageName, createdOn
     FROM page where mjc = 'ABC' ORDER BY createdOn DESC) t
WHERE mjc IN ('ABC')

---

这样可以避免运行同一子查询3次。同样的优化也可以用于

lastededid，lastedname，lastededidate

我想应该是这样的 但我不确定它会给你同样的结果。 当然，如果我看到结果，我会调整它。但举个例子：

---

---

我认为您还可以使用

max（）

来获得最后一次

modifiedOn

和

createdOn

而不是使用两个查询

希望它能帮助您尝试：

select m.mjc,
       m.name,
       s.*
from mags m
join 
(select mjc,
        max(case when cr_rn = 1 then pageID end) LastCreatedId,
        max(case when cr_rn = 1 then pageName end) LastCreatedName,
        max(case when cr_rn = 1 then createdOn end) LastCreatedDate,
        max(case when mo_rn = 1 then pageID end) LastEditedId,
        max(case when mo_rn = 1 then pageName end) LastEditedName,
        max(case when mo_rn = 1 then modifiedOn end) LastEditedDate,
        sum(case published when 1 then 1 else 0 end) PublishedPages,
        sum(case published when 0 then 1 else 0 end) UnpublishedPages
 from (select p.*,
             row_number() over (order by createdOn desc) cr_rn,
             row_number() over (order by modifiedOn desc) mo_rn,
       from page where mjc = 'ABC') pa
 group by mjc) s
on m.mjc=s.mjc
WHERE m.mjc IN ('ABC')

---

-对于单个页面的访问。如果要选择多个mjc值，请将

partitionbyMJC

添加到行数字段的

over

子句中。

Jeez，这可能是最佳解决方案，但可读性不强：-）太糟糕了，SQL Server不支持

FIRST\u VALUE（）

窗口函数。。。

select m.mjc,
       m.name,
       s.*
from mags m
join 
(select mjc,
        max(case when cr_rn = 1 then pageID end) LastCreatedId,
        max(case when cr_rn = 1 then pageName end) LastCreatedName,
        max(case when cr_rn = 1 then createdOn end) LastCreatedDate,
        max(case when mo_rn = 1 then pageID end) LastEditedId,
        max(case when mo_rn = 1 then pageName end) LastEditedName,
        max(case when mo_rn = 1 then modifiedOn end) LastEditedDate,
        sum(case published when 1 then 1 else 0 end) PublishedPages,
        sum(case published when 0 then 1 else 0 end) UnpublishedPages
 from (select p.*,
             row_number() over (order by createdOn desc) cr_rn,
             row_number() over (order by modifiedOn desc) mo_rn,
       from page where mjc = 'ABC') pa
 group by mjc) s
on m.mjc=s.mjc
WHERE m.mjc IN ('ABC')