八:子查询(where、having)

#进阶七:子查询 /* 说明:当一个查询语句中又嵌套了另一个完整的select语句,则被嵌套的select语句称为子查询或内查询 外面的select语句称为主查询或外查询。 分类: 按子查询出现的位置进行分类: 1、select后面     要求:子查询的结果为单行单列(标量子查询) 2、from后面     要求:子查询的结果可以为多行多列 3、where或having后面 ★     要求:子查询的结果必须为单列         单行子查询         多行子查询 4、exists后面     要求:子查询结果必须为单列(相关子查询)     特点:     1、子查询放在条件中,要求必须放在条件的右侧     2、子查询一般放在小括号中     3、子查询的执行优先于主查询     4、单行子查询对应了 单行操作符:> < >= <= = <>        多行子查询对应了 多行操作符:any/some  all in             #一、放在where或having后面 #一)单行子查询 #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salary>①的员工信息 SELECT last_name,salary 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 和工资 #①查询141号员工的job_id SELECT job_id FROM employees WHERE employee_id = 141 #②查询143号员工的salary SELECT salary FROM employees WHERE employee_id = 143 ③查询job_id=① and salary>②的信息 SELECT last_name,job_id,salary 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 #①查询最低工资 SELECT MIN(salary) FROM employees #②查询salary=①的员工的last_name,job_id和salary SELECT last_name,job_id,salary 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查询50号部门的最低工资 SELECT MIN(salary) FROM employees WHERE department_id = 50 #②查询各部门的最低工资,筛选看哪个部门的最低工资>① SELECT MIN(salary),department_id FROM employees GROUP BY department_id HAVING MIN(salary)>(     SELECT MIN(salary)     FROM employees     WHERE department_id = 50 ); 练习: #1. 查询和 Zlotkey 相同部门的员工姓名和工资 #①查询Zlotkey的部门编号 SELECT department_id FROM employees WHERE last_name = 'Zlotkey' #②查询department_id = ①的员工姓名和工资 SELECT last_name,salary FROM employees WHERE department_id = (     SELECT department_id     FROM employees     WHERE last_name = 'Zlotkey' ); #2. 查询工资比公司平均工资高的员工的员工号,姓名和工资。 #①查询平均工资 SELECT AVG(salary) FROM employees #②查询salary>①的信息 SELECT employee_id,last_name,salary FROM employees WHERE salary>(     SELECT AVG(salary)     FROM employees );                                                                                 #二)多行子查询 /* in:判断某字段是否在指定列表内   x  in(10,30,50) any / some:判断某字段的值是否满足其中任意一个 x>any(10,30,50)      等价于      x>min() x=any(10,30,50)      等价于      x in(10,30,50) all:判断某字段的值是否满足里面所有的 x >all(10,30,50)        等价于     x >max() */ #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 SELECT department_id FROM departments WHERE location_id IN(1400,1700) #②查询department_id = ①的姓名 SELECT last_name 员工姓名 FROM employees WHERE department_id IN(     SELECT DISTINCT department_id     FROM departments     WHERE location_id IN(1400,1700) ); #题目:返回其它部门中比job_id为‘IT_PROG’部门任一工资低的员工的员工号、姓名、job_id 以及salary #①查询job_id为‘IT_PROG’部门的工资 SELECT DISTINCT salary FROM employees WHERE job_id = 'IT_PROG' #②查询其他部门的工资<任意一个①的结果 SELECT employee_id,last_name,job_id,salary FROM employees WHERE salary<ANY(     SELECT DISTINCT salary     FROM employees     WHERE job_id = 'IT_PROG' ); 等价于 SELECT employee_id,last_name,job_id,salary FROM employees WHERE salary<(     SELECT MAX(salary)     FROM employees     WHERE job_id = 'IT_PROG' ); #案例3:返回其它部门中比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查询job_id为‘IT_PROG’部门的工资 SELECT DISTINCT salary FROM employees WHERE job_id = 'IT_PROG' #②查询其他部门的工资<所有①的结果 SELECT employee_id,last_name,job_id,salary FROM employees WHERE salary<ALL(     SELECT DISTINCT salary     FROM employees     WHERE job_id = 'IT_PROG' ); 等价于 SELECT employee_id,last_name,job_id,salary FROM employees WHERE salary<(     SELECT MIN(salary)     FROM employees     WHERE job_id = 'IT_PROG' );                                                   #二、放在select后面 #案例;查询部门编号是50的员工个数 #方式一;   SELECT COUNT(*)   FROM `employees`   WHERE `department_id`=50; #方式二:  SELECT   (      SELECT COUNT(*)      FROM employees      WHERE department_id = 50 )  个数;     #三、放在from后面 #案例:查询每个部门的平均工资的工资级别 #①查询每个部门的平均工资   SELECT AVG(salary),department_id   FROM employees   GROUP BY department_id #②将①和sal_grade两表连接查询   SELECT dep_ag.department_id,dep_ag.ag,g.grade   FROM sal_grade g   JOIN (      SELECT AVG(salary) ag,department_id       FROM employees       GROUP BY department_id ) dep_ag ON dep_ag.ag BETWEEN g.min_salary AND g.max_salary; #四、放在exists后面 #案例1 :查询有无名字叫“Abel”的员工信息   SELECT EXISTS(       SELECT *        FROM employees       WHERE last_name = 'Abel'  ) 有无Abel; #案例2:查询没有女朋友的男神信息   USE girls;   SELECT bo.*   FROM boys bo   WHERE bo.`id` NOT IN(       SELECT boyfriend_id       FROM beauty b  )                                                  
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