与测试共存，与朋友共勉！
SQL语句实例 5
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6.5外连接查询
select student.sno，sname，ssex，sage，sdept，cno，grade
from student，sc
where student.sno = sc.sno(*)
6.6复合条件连接查询
select student.sno, student.sname
from student, sc
where student.sno = sc.sno and sc.cno= ' 2 ' and sc.grade > 90
七．嵌套查询
7.1带有in谓词的子查询
select sno，sname③最后在student关系中
from student取出sno和sname
where sno in
(select sno②然后在sc关系中找出选
from sc修了3号课程的学生学号
where cno in
(select cno①首先在course关系中找出“信
from course息系统”的课程号，结果为3号
where cname= ‘信息系统’));
7.2带有比较运算符的子查询
select sno，sname，sdept
from student
where sdept =
select sdept
from student
where sname= '刘晨'；
7.3带有any（某个）或all（任何一个）谓词的子查询
用all谓词select sname，sage
from student
where sage < all
(select sage
from student
where sdept= ' is ') and sdept <> ' is ’;
用集函数select sname，sage
from student
where sage <
(select min(sage)
from student
where sdept= ' is ') and sdept <>' is
7.4带有exists谓词的子查询
select sname
from student
where not exists
(select *
from sc
where sno = student.sno and cno='1')；
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