选择两个表的差异

Question

我正在尝试做一些我认为应该有点简单的事情。我有两个选择语句：

1. SELECT concat(st.fname,' ',st.lname) as Fullname, st.parent_phone FROM student as st, grade as g, section as s, semester as sem WHERE st.studentid=g.studentid AND g.sectionid=s.sectionid AND s.semesterid=sem.semesterid AND s.semesterid not in (3, 4) Group by Fullname;

它返回这个（模拟数据）：

SELECT concat(st.fname,' ',st.lname) as Fullname, st.parent_phone FROM student as st, grade as g, section as s, semester as sem WHERE st.studentid=g.studentid AND g.sectionid=s.sectionid AND s.semesterid=sem.semesterid AND s.semesterid in (3, 4) Group by Fullname;

然后返回t他：

我希望做的是显示三个记录出现在第一条语句，但不是在按字母顺序排列的第二条语句。我想基本上从语句1中减去语句2中的所有记录。有人可以帮助我吗？

Answer 1

尝试：

SELECT x.* 
FROM (
    -- the first subquery goes here 
) x 
LEFT JOIN (
    -- the second subquery goes here 
) y 
ON x.full_name = y.full_name AND x.parent_phone = y.parent_phone 
WHERE y.parent_phone IS NULL