sql 面试基础 必会

#1
SELECT count(t_name) FROM teacher WHERE t_name like '李%';

#2
SELECT  DISTINCT sid,Sname,COUNT(expr) FROM student
--  3
SELECT student.*,score FROM sc LEFT JOIN student on sc.Sid=student.Sid 
WHERE cid=1 and score <(SELECT score FROM sc as p where p.sid=sc.sid and cid=2);


-- INSERT course VALUEs(7,'生物',7)
-- SELECT * FROM course
-- SELECT * FROM sc WHERE 
-- (SELECT *,tid FROM teacher WHERE Tname ='abc' ) not in
-- 
-- 
-- (SELECT cid FROM sc as p WHERE  p.sid=sc.Sid GROUP BY sid,cid )

-- 4SELECT * FROM student WHERE
 

SELECT * FROM student WHERE 
(SELECT cid FROM course WHERE tid=
(SELECT tid FROM teacher WHERE tname='张三' )) not in (
SELECT cid FROM sc WHERE sid=student.sid );

#5
SELECT * FROM course
SELECT * FROM student WHERE sid in
  ( SELECT if(COUNT( cid)<5,Sid,-1) FROM sc GROUP BY sid  );

# 6 
SELECT * FROM sc GROUP BY 

SELECT student.*,AVG(score) FROM student RIGHT JOIN sc on student.Sid=sc.Sid WHERE student.sid in
(SELECT if(sum( score <60)>=2,sid,-1) FROM sc GROUP BY sid )  GROUP BY sid;

7.ALTER
SELECT NULL 课程id,null 课程neme,null  最高分,null  最低分,null 平均分,null 及格,null 中等率,null 及格率 FROM sc




9
 SELECT *
FROM sc  WHERE ( SELECT sum(score>sc.score) FROM sc as p WHERE cid=sc.cid GROUP BY cid LIMIT 1
) <3 GROUP BY cid,sid  

 ORDER BY score DESC ;

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