Question

我有两个mySQL表：

tblcoach：包含字段（coachid，coachschoolid，otherstuff）

tblschool：包含字段（schoolid，schooldivision）

我正在努力获得一份学校名单，这些名单仅限于那些与教练处于同一学位的学校。

这段代码我的工作原理，但是有时会产生一个mySQL查询来实现相同的结果吗？

SELECT @cs := coachschoolid FROM tblcoach c;
SELECT @sd := s.schooldivision FROM tblschool s WHERE s.schoolid = @cs;
SELECT s2.schoolid, s2.schoolname FROM tblschool s2 WHERE schooldivision = @sd

Answer 1

嵌套查询：

select schoolId, schoolname
from tblschool
where 
    schooldivision = (
        select schooldivision from tblschool where schoolid = (
            select coachschoolid from tblcoach
        )
    )

Answer 2

这似乎只适用于1名教练。您可以使用自联接来执行此操作：

SELECT s2.schoolid, s2.schoolname 
FROM tblschool s
INNER JOIN tblschool s2 on s.schooldivision = s2.schooldivision
WHERE s.schoolid = ?

允许您传入schoolID。如果你想传入coachID：

SELECT s2.schoolid, s2.schoolname 
FROM tblschool s
INNER JOIN tblschool s2 on s.schooldivision = s2.schooldivision
INNER JOIN tblcoach c on c.coachschoolid = s.schoolid
WHERE c.coachid = ?

mySQL将多个查询更改为单个查询

2 个答案: