mysql - 合并两个选择查询

我想把这两个Select查询合并成一个查询。我该怎么做？

 SELECT link_id, COUNT(*)  FROM Loc  GROUP BY link_id

     SELECT Slink.[xlink:Show],Loc.[xlink:show],
     Slink.[xlink:actuate],Loc.[xlink:actuate] ,
     href, Sem.SemRoleDescrip
     FROM Sem  JOIN Loc  ON
     Sem.SemRoleId = Loc.SemRoleId
  JOIN Slink ON Slink.link_id = Loc.link_id

最佳答案

一个解决办法是
将COUNT语句添加为子查询
(LEFT) JOIN此子选择带有SLink表
将LinkCount添加到选定值列表中。
SQL语句

SELECT  Slink.[xlink:Show]
        , Loc.[xlink:show]
        , Slink.[xlink:actuate]
        , Loc.[xlink:actuate]
        , href
        , Sem.SemRoleDescrip
        , SLinkCount.LinkCount
FROM    Sem
        JOIN Loc ON Sem.SemRoleId = Loc.SemRoleId
        JOIN Slink ON Slink.link_id = Loc.link_id
        LEFT JOIN (
          SELECT  link_id, COUNT(*) AS LinkCount
          FROM    Loc
          GROUP BY
                  link_id
        ) SLinkCount ON SLinkCount.link_id = Slink.link_id

您可能需要阅读reference manual中的子查询
12.2.9.8条。FROM子句中的子查询
子查询在SELECT语句的FROM子句中是合法的。实际的
语法为：
SELECT ... FROM (subquery) [AS] name ...
name子句是必需的，因为a[AS]
子句必须有名称。子查询选择列表中的任何列都必须
有唯一的名字。