笔试题-sql语句

今天遇到了不熟练（不会）的查询题目

• 回来自己又做了一下，如下

建表语句

---

-- Table structure for score

---

DROP TABLE IF EXISTS score;
CREATE TABLE score (
id int(11) DEFAULT NULL,
sno int(11) DEFAULT NULL,
name varchar(255) DEFAULT NULL,
subject varchar(255) DEFAULT NULL,
score varchar(255) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

---

-- Records of score

---

INSERT INTO score VALUES ('1', '201201', '小明', 'math', '90');
INSERT INTO score VALUES ('2', '201202', '小李', 'math', '99');
INSERT INTO score VALUES ('3', '201203', '小红', 'math', '43');
INSERT INTO score VALUES ('4', '201201', '小明', 'en', '66');
INSERT INTO score VALUES ('5', '201202', '小李', 'en', '56');
INSERT INTO score VALUES ('6', '201203', '小红', 'en', '88');
INSERT INTO score VALUES ('7', '201201', '小明', 'computer', '99');
INSERT INTO score VALUES ('8', '201202', '小李', 'computer', '65');
INSERT INTO score VALUES ('9', '201203', '小红', 'computer', '67');
INSERT INTO score VALUES ('11', '201204', '小白', 'sss', '99');
INSERT INTO score VALUES ('11111', '201203', '小红', 'computer', '67');

• 题目1：找到所有分数都及格（>=60）的学生。

  1. 查询有科目分数小于 60 的， 然后 not in 即可
     select name from score where sno not in
     (select s.sno from score s where s.score < 60) GROUP BY sno

  2. not exists 写法
     select name from score s1 where not exists
     (select 1 from score s where s.score < 60 and s1.sno = s.sno) GROUP BY s1.sno

  3. having 筛选
     select * from score s GROUP BY s.sno having min(s.score) >= 60

• 题目2：表中有冗余记录，如何删除？如下图：

分析：找到该数据对应的id，根据id删除！

select s.id from score s group by s.sno,s.name,s.subject,s.score -- 此结果不包含需要删除的id
本以为是：delete from score where id not in (select s.id from score s group by s.sno,s.name,s.subject,s.score )

• 结果毫不犹豫的抛出错误：
  

• 查明原因，mysql认为delete/update 跟 子句里面select到的不能是一张表

• 做出改进（表起别名，按照需要删掉新插入的或者后插入的）

delete from score where id not in (select id from (select min(id) id from score s group by sno,name,subject,score )t)