[大数据] MySQL之子查询

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[大数据]MySQL之子查询

#子查询
#需求 谁的工资比Able高
#由一个具体的需求，引入子查询
#方式一
SELECT last_name,salary
FROM employees
WHERE last_name = 'Abel';

SELECT last_name,salary
FROM employees
WHERE salary>11000;
#方式二 自连接
SELECT emp2.last_name,emp2.salary
FROM employees emp1,employees emp2
WHERE emp1.`last_name`='Abel' AND emp2.`salary`>emp1.salary ;#sql92的不等值连接

SELECT emp2.last_name,emp2.salary
FROM employees emp1 JOIN employees emp2
ON emp1.last_name='Abel'AND emp2.`salary`>emp1.`salary`;#sql99的不等值连接
#方式三 子查询 类似一个嵌套for循环
SELECT last_name,salary
FROM employees e 
WHERE e.`salary`>(
		  SELECT salary
		  FROM employees e
		  WHERE e.last_name ='Abel'
		 );
#称谓的规范：外查询（主查询）、内查询（子查询）		 
/*
子查询（内查询）在主查询之前一次执行完成。
子查询的结果被主查询（外查询）使用 。

注意事项
子查询要包含在括号内
将子查询放在比较条件的右侧
单行操作符对应单行子查询，多行操作符对应多行子查询*/		 

/*子查询的分类
角度1：从内查询返回的结果的条目数
单行子查询  vs  多行自查询


角度2：内查询是否被执行多次
相关子查询  和  不相关子查询


比如：相关子查询的需求：查询工资大于本部门平均工资的员工信息
不相关子查询的需求：查询工资大于本公司平均工资的员工信息。
*/
	 
#单行子查询
#单行操作符 =  !=  < <=  >  >= <>

#子查询的编写技巧（或步骤）：① 从里往外写  ② 从外往里写

#题目：查询工资大于149号员工工资的员工的信息
SELECT employee_id,last_name,salary
FROM employees e
WHERE e.`salary`>(
		  SELECT salary
		  FROM employees e	
		  WHERE e.`employee_id`='149'
		 );
#题目: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
/*
先查出141号的job_id
查出143号的薪资是多少
在查出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
*/
SELECT last_name,job_id,salary
FROM employees e
WHERE e.`job_id`=(
		SELECT job_id
		FROM employees e
		WHERE e.`employee_id`=141
		) 
AND e.`salary`>(
		SELECT salary
		FROM employees e
		WHERE e.`employee_id`=143	
		); 

#题目：返回公司工资最少的员工的last_name,job_id和salary
SELECT last_name,job_id,salary
FROM employees e
WHERE e.`salary`=(
		SELECT MIN(salary)
		FROM employees e
		);
/*
题目：查询与141号员工的manager_id和department_id相同的其他员工的employee_id，
manager_id，department_id
*/	
SELECT employee_id,manager_id,department_id
FROM employees e
WHERE e.`manager_id`=(
		     SELECT manager_id
		     FROM employees e
		     WHERE e.`employee_id`=141
		    )
 AND e.`department_id`=(
		      SELECT department_id	
		      FROM employees e
		      WHERE e.`employee_id`=141 
		     )
AND e.`employee_id`<>141;

#方式二：了解

SELECT employee_id,manager_id,department_id
FROM employees
WHERE (manager_id,department_id) = (
				    SELECT manager_id,department_id
			            FROM employees
				    WHERE employee_id = 141
				   )
AND employee_id <> 141;


#题目：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
SELECT department_id,MIN(salary)
FROM employees
GROUP BY department_id
HAVING MIN(salary)>(
		    SELECT MIN(salary)
		    FROM employees e
		    WHERE e.`department_id`=50
		    );
/*题目：显式员工的employee_id,last_name和location。其中，若员工department_id与location_id为1800
的department_id相同，则location为’Canada’，其余则为’USA’。*/
SELECT employee_id,last_name, CASE department_id WHEN (SELECT department_id FROM  departments d WHERE d.location_id=1800)THEN 'canada' 
							ELSE 'USA'END   "location"
FROM employees e;	 

#空值问题
SELECT last_name
FROM employees
WHERE employee_id NOT IN (
			SELECT manager_id
			FROM employees
			);
			
#非法使用子查询	
#错误 Subquery returns more than 1 row	返回多余一行的记录
SELECT employee_id, last_name
FROM employees
WHERE salary =(SELECT MIN(salary)#多条数据
		FROM employees
		GROUP BY department_id
		);


/*多行子查询

IN 等于列表中的任意一个
ANY 需要和单行比较操作符一起使用，和子查询返回的某一个值比较
ALL 需要和单行比较操作符一起使用，和子查询返回的所有值比较
SOME 实际上是ANY的别名，作用相同，一般常使用ANY
*/		
 #IN
SELECT employee_id, last_name
FROM employees
WHERE salary IN (SELECT MIN(salary)#多条数据
		FROM employees
		GROUP BY department_id
		);
#ANY					
#题目：返回其它job_id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
SELECT e.employee_id,e.last_name,e.job_id,e.salary
FROM employees e
WHERE e.job_id <> 'IT_PROG'
AND  salary < ANY (
	SELECT salary
	FROM employees
	WHERE job_id='IT_PROG'
		);	     
#题目：返回其它job_id中比job_id为‘IT_PROG’部门所有工资低的员工的员工号、姓名、job_id 以及salary			 
SELECT e.employee_id,e.last_name,e.job_id,e.salary
FROM employees e
WHERE e.`job_id`<> 'IT_PROG'
AND salary <ALL (
	SELECT e.salary
	FROM employees e
	WHERE e.`job_id`='IT_PROG'
	);
#题目：查询平均工资最低的部门id
#MySQL中聚合函数不能嵌套使用
SELECT department_id
FROM employees e
GROUP BY e.`department_id`
HAVING AVG(e.`salary`)<=ALL(
		SELECT AVG(salary)
		FROM employees 
		GROUP BY department_id
		);
#方式二
SELECT department_id
FROM employees e
GROUP BY e.`department_id`
HAVING AVG(e.`salary`)=(
		SELECT MIN(asl)
		FROM (
		SELECT AVG(e.salary) asl
		FROM employees e
		GROUP BY department_id
		) t_avg_sal
		);
#多行子查询 空值问题
SELECT last_name
FROM employees
WHERE employee_id  NOT IN (
			SELECT manager_id
			FROM employees
			);
#有null参与运算所以上面查询的结果为空
SELECT last_name
FROM employees
WHERE employee_id  NOT IN (
			SELECT manager_id
			FROM employees
			WHERE manager_id IS NOT NULL
			);
#题目：查询员工中工资大于本部门平均工资的员工的last_name,salary和其department_id
SELECT last_name,salary,department_id
FROM employees e1
WHERE salary >(
		SELECT AVG(salary)
		FROM employees e2
		WHERE e2.`department_id`=e1.`department_id`
		);
#用FROM来解决
SELECT e1.last_name,e1.salary,e1.department_id
FROM employees e1,(
		  SELECT department_id,AVG(salary) A_sal
		  FROM  employees   
		  GROUP BY department_id
		 )AS t_sal_avg 		
WHERE e1.department_id=t_sal_avg.department_id 
AND  e1.`salary`>t_sal_avg.A_sal;

#题目：查询员工的id,salary,按照department_name 排序
SELECT employee_id,salary
FROM employees e 
ORDER BY (
	  SELECT department_name
	  FROM departments d
	  WHERE e.`department_id`=d.`department_id`#第一条数据连接
	) ASC;

#结论：在SELECT中，除了GROUP BY 和 LIMIT之外，其他位置都可以声明子查询！
/*
SELECT ....,....,....(存在聚合函数)
FROM ... (LEFT / RIGHT)JOIN ....ON 多表的连接条件 
(LEFT / RIGHT)JOIN ... ON ....
WHERE 不包含聚合函数的过滤条件
GROUP BY ...,....
HAVING 包含聚合函数的过滤条件
ORDER BY ....,...(ASC / DESC )
LIMIT ...,....
*/

#题目：若employees表中employee_id与job_history表中employee_id相同的数目不小于2，
#输出这些相同id的员工的employee_id,last_name和其job_id
SELECT *
FROM job_history;

SELECT employee_id,last_name,job_id
FROM employees e
WHERE 2 =<(
	   SELECT COUNT(*)
	   FROM job_history j
	   WHERE e.`employee_id`= j.`employee_id`	
	  );
	  
 # EXISTS 与 NOT EXISTS关键字
 
 /*
 EXISTS 与 NOT EXISTS关键字
关联子查询通常也会和 EXISTS操作符一起来使用，用来检查在子查询中是否存在满足条件的行。

如果在子查询中不存在满足条件的行：
条件返回 FALSE
继续在子查询中查找

如果在子查询中存在满足条件的行：
不在子查询中继续查找
条件返回 TRUE
 */ 
 
#题目：查询公司管理者的employee_id，last_name，job_id，department_id信息 

#方式一 自连接
SELECT DISTINCT mrg.employee_id,mrg.last_name,mrg.department_id
FROM employees emp,employees mrg
WHERE emp.`manager_id`=mrg.`employee_id`; 

#方式二 子查询
SELECT employee_id,last_name,department_id
FROM employees e
WHERE  e.`employee_id`IN(
			SELECT DISTINCT manager_id
			FROM employees
			);
 
 
#方式三 使用EXISTS
SELECT DISTINCT employee_id,last_name,department_id
FROM employees e
WHERE  EXISTS (
		SELECT * #返回的是查询的记录   这里写什么都行
		FROM employees e1
		WHERE e.employee_id=e1.`manager_id`
	);
	

 #题目：查询departments表中，不存在于employees表中的部门的department_id和department_name
#方式一
SELECT DISTINCT d.department_id,d.department_name
FROM employees e RIGHT JOIN departments d
ON e.`department_id`=d.`department_id`
WHERE e.`department_id` IS NULL;

#方式二
SELECT department_id,department_name
FROM departments d
WHERE  NOT EXISTS (
		SELECT *
		FROM  employees d1
		WHERE d.`department_id`=d1.`department_id`
	      );
	      
#子查询之课后习题
#1.查询和Zlotkey相同部门的员工姓名和工资
SELECT last_name,salary,department_id
FROM employees e
WHERE e.`department_id`=(
			SELECT e.department_id
			FROM departments d JOIN employees e
			ON e.`department_id`=d.`department_id`
			AND e.`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。
SELECT employee_id,last_name,salary
FROM employees
WHERE salary>(
	        SELECT AVG(salary)
		FROM employees
		);
		
#3.选择工资大于所有JOB_ID = 'SA_MAN'的员工的工资的员工的last_name, job_id, salary
SELECT last_name,job_id,salary
FROM employees e
WHERE e.`salary`>ALL(
		SELECT salary
		FROM employees e
		WHERE e.`job_id`='SA_MAN'
		     );	
		     
#4.查询和姓名中包含字母u的员工在相同部门的员工的员工号和姓名
SELECT employee_id,last_name
FROM employees e 
WHERE e.`department_id`IN(
			SELECT  department_id
			FROM employees e
			WHERE e.last_name LIKE '%u%'
			);

#5.查询在部门的location_id为1700的部门工作的员工的员工号
SELECT last_name,employee_id,location_id
FROM employees  e JOIN departments d
ON e.`department_id`=d.`department_id`
WHERE d.`location_id`=1700;


#6.查询管理者是King的员工姓名和工资
SELECT e1.last_name,e1.salary
FROM employees e1 
WHERE e1.`manager_id`IN(
			SELECT e.employee_id
			FROM employees e
			WHERE e.`last_name`='King'
			);
#方式二 自连接加EXISTS
SELECT 
FROM employees e
WHERE EXISTS(	
		
	     )
		

			
#7.查询工资最低的员工信息: last_name, salary
SELECT last_name,salary
FROM employees e
WHERE e.salary=(
		SELECT MIN(salary)
		FROM employees e
		);

#8.查询平均工资最低的部门信息
#方式一
SELECT department_id,AVG(salary)
FROM employees e
GROUP BY department_id
HAVING AVG(salary)<=ALL(
		SELECT AVG(e.salary)
		FROM employees e
		GROUP BY  department_id
		);
#方式二
SELECT *
FROM departments
WHERE department_id = (
		SELECT department_id
		FROM employees e
		GROUP BY department_id
		HAVING AVG(salary)=(
				     SELECT MIN(avg_sal)
				     FROM(
				          SELECT AVG(salary) avg_sal
				          FROM employees e
				          GROUP BY department_id
				         )t_dept_avg_sal
				   )
			);
#方式三 LIMIT
SELECT *
FROM departments d
WHERE d.`department_id`=(
			SELECT department_id
			FROM employees e
			GROUP BY e.`department_id`
			HAVING AVG(e.`salary`)=(
						SELECT AVG(salary)AS avg_sal
						FROM employees e
						GROUP BY e.`department_id`
						ORDER BY avg_sal ASC
						LIMIT 0,1
						)
			);
#第四种方式
SELECT d.*
FROM departments d,(
			SELECT department_id,AVG(salary)AS avg_sal
			FROM employees
			GROUP BY department_id
			ORDER BY avg_sal ASC
			LIMIT 0,1 
			)AS t_d
WHERE d.`department_id`=t_d.department_id;



#9.查询平均工资最低的部门信息和该部门的平均工资（相关子查询）

SELECT d.*,AVG(e.`salary`)AS avg_sal
FROM departments d JOIN employees e
ON d.`department_id`=e.`department_id`
WHERE d.`department_id`=(
			SELECT department_id
			FROM employees e
			GROUP BY e.`department_id`
			HAVING AVG(e.`salary`)=(
						SELECT  MIN(avg_sal)
						FROM (
							SELECT AVG(salary)AS avg_sal
							FROM employees e
							GROUP BY e.`department_id`
						        )AS t_avg_s
						)

			);
#10.查询平均工资最高的 job 信息
SELECT job_id,salary
FROM employees e
GROUP BY e.`job_id`
HAVING MAX(salary)=(
		SELECT MAX(salary)AS max_sal
		FROM employees e
		GROUP BY job_id
		ORDER BY max_sal DESC
		LIMIT 0,1
		);
#方式二

SELECT *
FROM jobs
WHERE job_id=(
		SELECT job_id
		FROM employees e
		GROUP BY job_id
		HAVING AVG(salary)=(SELECT MAX(avg_sal)
					FROM (
					SELECT AVG(salary)AS avg_sal
					FROM employees e
					GROUP BY e.`job_id`		
					)AS t_avg
				
				)
		);
#方式三
SELECT *
FROM jobs j
WHERE j.`job_id`=(
		SELECT job_id
		FROM employees
		GROUP BY job_id
		HAVING  AVG(salary)>=ALL(#大于等于取最大值
					SELECT AVG(salary)
					FROM employees e
					GROUP BY e.`job_id`
					)
		)
#第四种方式
SELECT jobs.*
FROM jobs JOIN (
		SELECT job_id,AVG(salary)
		FROM employees
		GROUP BY job_id
		ORDER BY salary DESC
		LIMIT 0,1#取出salary最大的一条记录 在from里充当表结构 和jobs表连接 因为此时表中只有一条记录 
		)t_avgta
ON jobs.`job_id`=t_avgta.job_id						
#11.查询平均工资高于公司平均工资的部门有哪些?
SELECT department_id,AVG(salary)
FROM employees e
WHERE e.`department_id` IS NOT NULL
GROUP BY department_id
HAVING AVG(salary)>(
		   SELECT AVG(salary)
		    FROM employees e
		    );
#12.查询出公司中所有 manager 的详细信息
#方式一:自连接
SELECT DISTINCT e2.employee_id,e2.last_name,e2.`job_id`,e2.department_id
FROM employees e1,employees e2
WHERE e1.`manager_id`=e2.`employee_id`;

#方式二:子查询
SELECT last_name,employee_id,salary,job_id
FROM employees e
WHERE e.`employee_id`IN (
			SELECT DISTINCT manager_id
			FROM employees 
			);
#方式三 EXISTS
SELECT last_name,employee_id,salary,job_id
FROM employees e
WHERE EXISTS(
	     SELECT DISTINCT manager_id
	     FROM employees e2
	     WHERE e.`employee_id`=e2.`employee_id` #从第一层select语句进入一条记录匹配二层select所有记录 记录匹配则打印
	    );
#13.各个部门中 最高工资中最低的那个部门的最低工资是多少?
#方式一
SELECT MIN(salary)
FROM employees e
WHERE e.`department_id`=(
			SELECT department_id
			FROM employees e
			GROUP BY e.`department_id`
			HAVING MAX(e.`salary`)=(
						SELECT MAX(salary)AS max_sal
						FROM employees e
						GROUP BY e.`department_id`
						ORDER BY max_sal ASC
						LIMIT 0,1
						)
			);
#方式二	
SELECT MIN(salary)
FROM employees e
WHERE e.`department_id`=(
			SELECT department_id
			FROM employees
			GROUP BY department_id
			HAVING MAX(salary)=(SELECT MIN(max_sal)#最底工资的部门和每个部门的最高工资匹配等于返回部门id
						FROM(
							SELECT MAX(salary)AS max_sal 
							FROM employees
							GROUP BY department_id
							)AS t_tables_max
					    )
			);			    
#方式三
SELECT MIN(salary)
FROM employees e
WHERE e.`department_id`=(
			SELECT department_id
			FROM employees
			GROUP BY department_id
			HAVING MAX(salary)<=ALL(#小于等于最小的前提是都是相同的聚合函数的值	
						SELECT MAX(salary)
						FROM employees
						GROUP BY department_id
						)		
					
			);					
#方式四
SELECT MIN(salary)
FROM employees e,(
		SELECT department_id,MAX(salary)AS max_sal
		FROM employees
		GROUP BY department_id
		ORDER BY max_sal ASC
		LIMIT 0,1						
		) AS t_desal
WHERE e.department_id=t_desal.department_id
					    
#14.查询平均工资最高的部门的 manager 的详细信息: last_name, department_id, email, salary
		SELECT employee_id,last_name, department_id, email, salary
		FROM employees
		WHERE employee_id IN (
					SELECT DISTINCT manager_id
					FROM employees
					WHERE department_id = (
								SELECT department_id
								FROM employees e
								GROUP BY department_id
								HAVING AVG(salary)>=ALL(
											SELECT AVG(salary)
											FROM employees
											GROUP BY department_id
											)
								)
					);
#方式二	
SELECT last_name, department_id, email, salary
FROM employees e
WHERE e.`employee_id`IN(#匹配
			SELECT employee_id#返回员工id
			FROM employees e
			GROUP BY department_id
			HAVING AVG(e.salary)=(
						SELECT MAX(avg_sal)
						FROM (
							SELECT AVG(salary)AS avg_sal
							FROM employees
							GROUP BY department_id
							)AS t_avg_sal			
						)
			);
#方式三
SELECT last_name, department_id, email, salary
FROM employees e
WHERE e.`employee_id`=(
			SELECT employee_id
			FROM employees e
			GROUP BY department_id
			HAVING AVG(e.`salary`)=(
						SELECT AVG(salary)AS avg_sal
						FROM employees e
						GROUP BY department_id
						ORDER BY avg_sal DESC
						LIMIT 0,1
						)
			);
#方式四
SELECT last_name, department_id, email, salary
FROM employees
WHERE employee_id IN(
			SELECT manager_id 
			FROM employees e,(
					SELECT department_id,AVG(salary)AS asl
					FROM employees
					GROUP BY department_id
					ORDER BY asl DESC
					LIMIT 0,1
					)AS t_dept_avg_sal
			WHERE e.`department_id`=t_dept_avg_sal.department_id
		);													
#15. 查询部门的部门号，其中不包括job_id是"ST_CLERK"的部门号
SELECT DISTINCT department_id,job_id
FROM employees
WHERE job_id <>'ST_CLERK'  AND department_id IS NOT NULL  

#方式二
SELECT DISTINCT  department_id,job_id
FROM employees e
WHERE e.department_id !=(
			SELECT DISTINCT department_id
			FROM employees
			WHERE job_id='ST_CLERK'
			);
#方式三		
SELECT department_id,job_id
FROM employees e
WHERE NOT EXISTS (#第一层select进去一条记录  在第二层匹配所有数据 不满足条件返回
		SELECT department_id
		FROM employees e2
		WHERE e.`department_id`=e2.`department_id` 
		AND e2.job_id='ST_CLERK'
		)					
					
#16. 选择所有没有管理者的员工的last_name
SELECT last_name
FROM  employees
WHERE manager_id IS NULL;
#方式二
SELECT last_name
FROM employees e
WHERE NOT EXISTS (
		SELECT *
		FROM employees e2
		WHERE e.`manager_id`=e2.`employee_id`
		);
#17．查询员工号、姓名、雇用时间、工资，其中员工的管理者为 'De Haan'
SELECT employee_id,last_name,hire_date,salary
FROM employees e
WHERE e.last_name IN(
		SELECT emp.last_name
		FROM employees emp JOIN employees mrg
		ON emp.`manager_id`=mrg.`employee_id`
		AND mrg.last_name='De Haan'
		);
#方式二
SELECT employee_id,last_name,hire_date,salary
FROM employees e
WHERE e.`manager_id`IN(
			SELECT employee_id
			FROM employees e
			WHERE e.`last_name`='De Haan'
			)
#方式三
SELECT employee_id,last_name,hire_date,salary
FROM employees e
WHERE EXISTS (
		SELECT employee_id
		FROM employees e2
		WHERE e.`manager_id`=e2.`employee_id`
		AND e2.last_name='De Haan'
		)

#18.查询各部门中工资比本部门平均工资高的员工的员工号, 姓名和工资（相关子查询）
SELECT employee_id,last_name,salary
FROM employees e1
WHERE e1.`salary`>(#员工工资比部门平均工资高
		SELECT AVG(salary)
		FROM employees e
		WHERE e1.`department_id`=e.`department_id`#匹配 返回 部门平均值		
		)
#方式二	
SELECT employee_id,last_name,salary
FROM employees e1
WHERE salary > (
		# 查询某员工所在部门的平均
		SELECT AVG(salary)
		FROM employees e2
		WHERE e2.department_id = e1.`department_id`
		);
#方式三
SELECT employee_id,last_name,salary
FROM employees e1,
	(
	SELECT department_id,AVG(salary) avg_sal
	FROM employees e2 GROUP BY department_id
	) dept_avg_sal
WHERE e1.`department_id` = dept_avg_sal.department_id
AND e1.`salary` > dept_avg_sal.avg_sal;
				
#19.查询每个部门下的部门人数大于 5 的部门名称（相关子查询）

SELECT department_name
FROM departments d
WHERE 5>(
	SELECT COUNT(*)
	FROM employees e
	WHERE d.`department_id`=e.`department_id`
	);
	
#20.查询每个国家下的部门个数大于 2 的国家编号（相关子查询）

SELECT country_id
FROM locations l
WHERE 2<(
	SELECT COUNT(*)
	FROM departments d
	WHERE l.`location_id`=d.`location_id`
	);
/* 
子查询的编写技巧（或步骤）：① 从里往外写  ② 从外往里写

如何选择？
① 如果子查询相对较简单，建议从外往里写。一旦子查询结构较复杂，则建议从里往外写
② 如果是相关子查询的话，通常都是从外往里写。

*/