MySQL中几种常见的嵌套查询详解

# 创建学员信息表 
CREATE TABLE stu_info
(
id INT AUTO_INCREMENT PRIMARY KEY, 
iname VARCHAR(20), 
gender CHAR(1), 
department VARCHAR(10), 
age TINYINT, 
province VARCHAR(10), 
email VARCHAR(50), 
mobilephone CHAR(11)
);
# 向学员表中插入数据 
INSERT INTO stu_info(iname,gender,department,age,province,email,mobilephone) VALUES 
('张勇','男','数学系',23,'河南','sfddf123dd@163.com','13323564321'), 
('王兵','男','数学系',25,'江苏','lss1993@163.com','17823774329'), 
('刘伟','男','计算机系',21,'江苏','qawsed112@126.com','13834892240'), 
('张峰','男','管理系',22,'上海','102945328@qq.com','13923654481'), 
('董敏','女','生物系',22,'浙江','82378339@qq.com','13428439022'), 
('徐晓红','女','计算机系',24,'浙江','xixiaohong@gmail.com','13720097528'), 
('赵伊美','女','数学系',21,'江苏','zhaomeimei@163.com','13417723980'), 
('王建国','男','管理系',24,'浙江','9213228402@qq.com','13768329901'), 
('刘清','女','统计系',23,'安徽','lq1128@gmail.com','17823651180'), 
('赵家和','男','计算机系',28,'山东','dcrzdbjh@163.com','13827811311');

# 创建学员成绩表 
CREATE TABLE stu_score( id INT , Excel TINYINT, Tableau TINYINT, MySQL TINYINT ); 
# 向成绩表中插入数据 
INSERT INTO stu_score VALUES 
(1,87,72,88), 
(3,90,66,72), 
(2,90,70,86), 
(4,88,82,76), 
(8,92,67,80), 
(10,88,82,89), 
(5,79,66,60), 
(7,91,78,90), 
(6,82,79,88), 
(9,85,70,85); 

# 1.查询年龄超过所有学员平均年龄的学员信息 
SELECT * FROM stu_info 
WHERE age >= avg(age); 
#需要注意的是Where后面不能使用聚合函数
#应该修改成
SELECT AVG(age) FROM stu_info;
SELECT * FROM stu_info
WHERE age>=23.3
#二合一 
# 1.查询年龄超过所有学员平均年龄的学员信息 
SELECT * FROM stu_info 
WHERE age >= (SELECT AVG(age) FROM stu_info);

# 2.查询年龄不低于所属系平均年龄的学员信息 
SELECT * FROM stu_info AS s1 
WHERE age>= ( SELECT avg(age) FROM stu_info AS s2 
			  WHERE s1.department = s2.department);

# 1.查询非管理系中比管理系任意一个学员年龄小的学员信息 
SELECT * FROM stu_info 
WHERE age < ANY(SELECT DISTINCT age FROM stu_info WHERE department = '管理系') 
			AND department != '管理系';

# 2.查询非管理系中比管理系所有学员年龄大的学员信息 
SELECT * FROM stu_info 
WHERE age > ALL (SELECT DISTINCT age FROM stu_info WHERE department = '管理系') 
      AND department != '管理系';

# 1.查询数学系和计算机系的学员信息 
SELECT * FROM stu_info WHERE department IN('数学系','计算机系'); 
# 2.查询与张勇、刘伟同一个系的学员信息 
SELECT * FROM stu_info 
WHERE department IN (SELECT department FROM stu_info WHERE iname IN('张勇','刘伟')); 
# 3.查询MySQL成绩大于85分的学员信息 
SELECT * FROM stu_info 
WHERE id IN (SELECT id FROM stu_score WHERE MySQL > 85);

# 查询MySQL成绩大于85分的学员信息 
SELECT * FROM stu_info 
WHERE EXISTS
(SELECT * FROM stu_score WHERE stu_score.id = stu_info.id AND MySQL > 85);

# 查询数学系和计算机系之外的学员信息 
# 方法一 
SELECT * FROM stu_info 
WHERE department NOT IN('数学系','计算机系'); 
#方法二 
SELECT * FROM stu_info 
WHERE NOT EXISTS(SELECT * FROM stu_score WHERE department IN('数学系','计算机系') and stu_score.id = stu_info.id); 
# not exists的逻辑比较复杂，需要大家慢慢领会 
# 主要看not exists括号中的sql语句是否有结果，无结果：才会继续执行where条件；有结果：视为 where条件不成立。 
# 当子查询和主查询有关联条件时，相当于从主查询中去掉子查询的数据。

         SELECT (SELECT s1 FROM t2) FROM t1;
         SELECT (SELECT s2 FROM t1);