MySql中子查询内查询示例详解_Mysql_

 #WHERE或HAVING后面 #1.标量子查询(单行子查询) #2.列子查询(多行子查询) #3.行子查询(多列多行) #特点: # ①子查询放在小括号内 # ②子查询一般放在条件的右侧 # ③标量子查询:一般搭配着单行操作符使用 # 单行操作符: >< >= <= <> !- # 列子查询，一般搭配着多行操作符使用 # IN,ANY/SOME(任意),ALL # ④子查询的执行优先与主查询执行,主查询的条件用到了子查询的结果。

 #1.标量子查询 #案例1:谁的工资比Abel高？ #①查询Abel的工资 SELECT salary FROM employees WHERE last_name = 'Abel';

 #②查询员工的信息，满足Salary>①结果 SELECT * FROM employees WHERE salary>(SELECT salary FROM employees WHERE last_name='Abel');

 #案例2.返回job_id与141号员工相同，salary比143号员工多的员工姓名，job_id,工资。 #①查141员工的job_id SELECT job_id FROM employees WHERE employee_id='141';

 #②查143员工的salary SELECT salary FROM employees WHERE employee_id='143';

 #③最后合并结果 SELECT CONCAT(last_name,first_name) AS 姓名, job_id AS 工种编号, salary AS 工资 FROM employees WHERE job_id=( SELECT job_id FROM employees WHERE employee_id='141' ) AND salary>( SELECT salary FROM employees WHERE employee_id='143' );

 #案例3.返回公司工资最少的员工的last_name,job_id和salary。 SELECT MIN(salary) FROM employees;

 SELECT last_name AS 姓, salary AS 工资, job_id AS 工种编号 FROM employees WHERE salary=( SELECT MIN(salary) FROM employees );

 #案例4.查询最低工资大于50号部门最低工资的部门id和其最低工资。 #①查50部门的最低工资 SELECT MIN(salary) FROM employees WHERE department_id=50;

 #分组后，筛选条件①.【不用排除没有部门的所以不筛选部门编号】 SELECT department_id AS 部门编号, MIN(salary) AS 月薪 FROM employees #WHERE department_id GROUP BY department_id HAVING 月薪>( SELECT MIN(salary) FROM employees );

 #2.列子查询(多行子查询) #返回多行 #使用多行比较操作符

 #案例1.返回location_id是1400或1700的部门中的所有员工姓名。 #①查询location_id是1400或1700的部门编号 SELECT DISTINCT department_id FROM departments WHERE location_id IN(1400,1700);

 #②查询员工姓名，要求部门号是①列表的某一个 SELECT CONCAT(last_name,first_name) AS 姓名 FROM employees WHERE department_id IN ( SELECT DISTINCT department_id FROM departments WHERE location_id IN(1400,1700) );

 用ANY替代IN与上面同样的结果 SELECT CONCAT(last_name,first_name) AS 姓名 FROM employees WHERE department_id = ANY( SELECT DISTINCT department_id FROM departments WHERE location_id IN(1400,1700) );

 #案例.返回location_id不是1400或1700的部门中的所有员工姓名。 SELECT CONCAT(last_name,first_name) AS 姓名 FROM employees WHERE department_id NOT IN( SELECT DISTINCT department_id FROM departments WHERE location_id IN(1400,1700) ); ============================== SELECT CONCAT(last_name,first_name) AS 姓名 FROM employees WHERE department_id <> ALL( SELECT DISTINCT department_id FROM departments WHERE location_id IN(1400,1700) );

 #案例2.返回其他工种中比job_id为IT_PROG部门任意一工资低的员工工号, # 姓名,job_id以及salary #①把IT_PROG部门中的工资查出来 SELECT DISTINCT salary FROM employees WHERE job_id='IT_PROG';

 #②把不是IT_PROG部门信息查出来 SELECT * FROM employees WHERE job_id != 'IT_PROG';

 #③合并①与②在员工表中查出来 SELECT employee_id AS 员工编号, CONCAT(last_name,first_name) AS 姓名, job_id AS 工种编号, salary AS 工资 FROM employees WHERE job_id != 'IT_PROG' AND salary

 用MAX代替ANY与上面同样的效果 SELECT employee_id AS 员工编号, CONCAT(last_name,first_name) AS 姓名, job_id AS 工种编号, salary AS 工资 FROM employees WHERE job_id <> 'IT_PROG' AND salary<( SELECT MAX(salary) FROM employees WHERE job_id='IT_PROG' );

 #案例3.返回其他部门中比job_id为‘IT_PROG'部门所有工资都低的员工 #的员工号，姓名，job_id以及salary。 #①先把IT_PROG部门的工资查出来。 SELECT DISTINCT salary FROM employees WHERE job_id='IT_PROG';

 SELECT employee_id AS 员工号, CONCAT(last_name,first_name) AS 姓名, job_id AS 工种编号, salary AS 工资 FROM employees WHERE salary 'IT_PROG'; ============================= MIN替代ALL SELECT employee_id AS 员工号, CONCAT(last_name,first_name) AS 姓名, job_id AS 工种编号, salary AS 工资 FROM employees WHERE salary<( 　　SELECT MIN(salary) 　　FROM employees 　　WHERE job_id='IT_PROG' ) AND job_id <> 'IT_PROG';

 #3.行子查询(结果集一行多列或者多行多列) #案例1.查询员工编号最小并且工资最高的员工信息.引入 SELECT MIN(employee_id) FROM employees; ================= SELECT MAX(salary) FROM employees;

 SELECT * FROM employees WHERE employee_id = ( SELECT MIN(employee_id) FROM employees ) AND salary = ( SELECT MAX(salary) FROM employees );

 这种查询结果使用虚拟字段，单行操作符必须一致可以使用。查出来与上面同样的效果。 SELECT * FROM employees WHERE (employee_id,salary)=( SELECT MIN(employee_id), MAX(salary) FROM employees );

 #二.SELECT子查询 #仅仅支持标量子查询，结果是一行一列 #案例1.查询每个部门的员工个数 SELECT d.*,(SELECT COUNT(*) FROM employees) FROM departments d; 

 添加条件 SELECT d.*,(SELECT COUNT(*) FROM employees e WHERE e.department_id=d.department_id ) AS 个数 FROM departments d; 

 #案例2.查询员工号=102的部门名。 SELECT department_name FROM departments; ============== SELECT employee_id FROM employees WHERE employee_id = 102;

 SELECT employee_id, ( SELECT department_name FROM departments d WHERE e.department_id=d.department_id ) FROM employees e WHERE employee_id=102;

 #三.FROM 后面 注意:将子查询结果充当一张表，要求必须起别名 #案例:查询每个部门的平均工资等级。 SELECT ROUND(AVG(salary),2),department_id FROM employees GROUP BY department_id;

 SELECT e.平均工资,j.grade_level FROM job_grades AS j ,( SELECT ROUND(AVG(salary),2) AS 平均工资,department_id FROM employees GROUP BY department_id ) AS e WHERE e.平均工资 BETWEEN j.lowest_sal AND j.highest_sal;提示：
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