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Mysql —— 6、子查询_mysql salary语句

作者：Guff_9hys | 2024-08-11 06:42:15

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mysql salary语句

目录

1、子查询的基本使用及分类

1.1、子查询的基本使用

1.2、子查询的分类

2、单行子查询

2.1、单行子查询比较操作符

 2.2、代码示例

2.3、HAVING中的子查询

2.4、CASE中的子查询

2.5、子查询中的空值问题

3、多行子查询

3.1、多行比较操作符

3.2、代码示例 

4、相关子查询

4.1、相关子查询执行过程

4.2、代码示例

4.3、EXISTS 与 NOT EXISTS关键字

4.4、相关更新

4.5、相关删除

5、关于自连接和子查询效率问题

6、练习

子查询指一个查询语句嵌套在另一个查询语句内部的查询，这个特性从MySQL 4.1开始引入。

SQL 中子查询的使用大大增强了 SELECT 查询的能力，因为很多时候查询需要从结果集中获取数据，或者需要从同一个表中先计算得出一个数据结果，然后与这个数据结果（可能是某个标量，也可能是某个集合）进行比较。

1、子查询的基本使用及分类

1.1、子查询的基本使用

  • 子查询的基本语法结构：括号内为内查询（子查询），括号外为外查询（主查询）

  • 在SELECT中，除了GROUP BY 和 LIMIT之外，其他位置都可以声明子查询

  • 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

1.2、子查询的分类

1、按内查询的结果返回一条还是多条记录，将子查询分为单行子查询、多行子查询。

2、按内查询是否被执行多次，将子查询划分为相关(或关联)子查询和不相关(或非关联)子查询。

        子查询从数据表中查询了数据结果，如果这个数据结果只执行一次，然后这个数据结果作为主查询的条件进行执行，那么这样的子查询叫做不         相关子查询。

        同样，如果子查询需要执行多次，即采用循环的方式，先从外部查询开始，每次都传入子查询进行查询，然后再将结果反馈给外部，这种嵌套         的执行方式就称为相关子查询。

2、单行子查询

2.1、单行子查询比较操作符

 2.2、代码示例

  1. #题目：查询工资大于149号员工工资的员工的信息
  2. SELECT employee_id, last_name, salary
  3. FROM employees
  4. WHERE salary > (
  5. 		SELECT salary
  6. 		FROM employees
  7. 		WHERE employee_id = 149
  8. 		);
  9.  
  10. #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
  11. SELECT last_name, job_id, salary
  12. FROM employees
  13. WHERE job_id = (
  14. 		SELECT job_id
  15. 		FROM employees
  16. 		WHERE employee_id = 141
  17. 		)
  18. AND salary > (
  19. 	      SELECT salary
  20. 	      FROM employees
  21. 	      WHERE employee_id = 143
  22. 	      );
  23.  
  24.  
  25. #题目：返回公司工资最少的员工的last_name,job_id和salary
  26. SELECT last_name, job_id, salary
  27. FROM employees
  28. WHERE salary = (
  29. 		SELECT MIN(salary)
  30. 		FROM employees
  31. 		);
  32.  
  33.  
  34. #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。
  35. #方式1:
  36. SELECT employee_id, manager_id, department_id
  37. FROM employees
  38. WHERE manager_id = (
  39. 		SELECT manager_id
  40. 		FROM employees
  41. 		WHERE employee_id = 141
  42. 		)
  43. AND department_id = (
  44. 		SELECT department_id
  45. 		FROM employees
  46. 		WHERE employee_id = 141
  47. 		)
  48. AND employee_id <> 141;
  49. #方式2：了解
  50. SELECT employee_id,manager_id,department_id
  51. FROM employees
  52. WHERE (manager_id,department_id) = (
  53. 				    SELECT manager_id,department_id
  54. 			            FROM employees
  55. 				    WHERE employee_id = 141
  56. 				   )
  57. AND employee_id <> 141;

2.3、HAVING中的子查询

  • 首先执行子查询。

  • 向主查询中的HAVING 子句返回结果

  1. #题目：查询最低工资大于110号部门最低工资的部门id和其最低工资
  2. SELECT department_id, MIN(salary)
  3. FROM employees
  4. WHERE department_id IS NOT NULL
  5. GROUP BY department_id
  6. HAVING MIN(salary) > (
  7. 			SELECT MIN(salary)
  8. 			FROM employees
  9. 			WHERE department_id = 110
  10. 			);

2.4、CASE中的子查询

  1. SELECT employee_id,last_name,CASE department_id WHEN(SELECT department_id
  2. 						     FROM departments
  3. 						     WHERE location_id = 1800) THEN 'Canada'
  4. 						     ELSE 'USA' END "location"
  5. FROM employees

2.5、子查询中的空值问题

子查询不返回任何行，主查询也不返回任何行

  1. SELECT last_name, job_id
  2. FROM   employees
  3. WHERE  job_id =
  4.                  #子查询中空值
  5.                 (SELECT job_id
  6.                  FROM   employees
  7.                  WHERE  last_name = 'Haas');

3、多行子查询

  • 也称为集合比较子查询

  • 内查询返回多行

  • 使用多行比较操作符

3.1、多行比较操作符

3.2、代码示例 

1、IN

  1. SELECT employee_id, last_name
  2. FROM   employees
  3. WHERE  salary IN
  4.                 (SELECT   MIN(salary)
  5.                  FROM     employees
  6.                  GROUP BY department_id);

2、ANY

  1. #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
  2. SELECT employee_id, last_name, job_id, salary
  3. FROM employees
  4. WHERE job_id <> 'IT_PROG'
  5. AND salary < ANY(
  6. 		SELECT salary
  7. 		FROM employees
  8. 		WHERE job_id = 'IT_PROG'
  9. 		);

3、ALL

  1. #题目：查询平均工资最低的部门id
  2. #MySQL中聚合函数是不能嵌套使用的。
  3. #方式1：
  4. SELECT department_id
  5. FROM employees
  6. GROUP BY `department_id`
  7. HAVING AVG(salary) = (
  8. 			SELECT MIN(avg_sal)
  9. 			FROM (
  10. 				SELECT AVG(salary) avg_sal
  11. 				FROM employees
  12. 				GROUP BY department_id
  13. 				) t_dept_avg_sal
  14. 		      );
  15. #方式2：
  16. SELECT department_id
  17. FROM employees
  18. GROUP BY `department_id`
  19. HAVING AVG(salary) <= ALL(
  20. 		SELECT AVG(salary)
  21. 		FROM employees
  22. 		GROUP BY department_id
  23. 		)

4、相关子查询

4.1、相关子查询执行过程

如果子查询的执行依赖于外部查询，通常情况下都是因为子查询中的表用到了外部的表，并进行了条件关联，因此每执行一次外部查询，子查询都要重新计算一次，这样的子查询就称之为关联子查询。

相关子查询按照一行接一行的顺序执行，主查询的每一行都执行一次子查询。

说明：子查询中使用主查询中的列  

4.2、代码示例

  1. #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
  2. #方式1：使用相关子查询
  3. SELECT last_name, salary, department_id
  4. FROM employees e1
  5. WHERE salary > (
  6. 	SELECT AVG(salary)
  7. 	FROM employees e2
  8. 	WHERE department_id = e1.department_id
  9. 	);
  10. #方式2：在FROM中声明子查询
  11. SELECT e1.last_name, e1.salary, e1.department_id
  12. FROM employees e1, (
  13. 		SELECT department_id, AVG(salary) avg_sal
  14. 		FROM employees e2
  15. 		GROUP BY `department_id`
  16. 		) e2
  17. WHERE e1.department_id = e2.department_id
  18. AND e1.salary > avg_sal
  1. #题目：查询员工的id,salary,按照department_name 排序
  2. SELECT employee_id, salary
  3. FROM `employees` e
  4. ORDER BY (
  5. 	SELECT `department_name`
  6. 	FROM `departments` d
  7. 	WHERE e.department_id = d.department_id
  8. 	);
  1. #题目：若employees表中employee_id与job_history表中employee_id相同的数目不小于2，
  2. #输出这些相同id的员工的employee_id,last_name和其job_id
  3. SELECT e.employee_id, e.last_name, e.job_id
  4. FROM employees e
  5. WHERE 2 <= (
  6. 	SELECT COUNT(*)
  7. 	FROM `job_history` j
  8. 	WHERE j.employee_id = e.employee_id
  9. 	);

4.3、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

  • NOT EXISTS关键字表示如果不存在某种条件，则返回TRUE，否则返回FALSE。

1、EXISTS

  1. #题目：查询公司管理者的employee_id，last_name，job_id，department_id信息
  2. #方式1：自连接
  3. SELECT DISTINCT m.employee_id, m.last_name, m.job_id, m.department_id
  4. FROM employees e JOIN employees m
  5. ON e.manager_id = m.employee_id;
  6. #方式2：子查询
  7. SELECT e.employee_id, e.last_name, e.job_id, e.department_id
  8. FROM employees e
  9. WHERE e.`employee_id` IN(
  10. 		SELECT DISTINCT m.manager_id
  11. 		FROM employees m
  12. 		);
  13. #方式3：使用EXISTS
  14. SELECT e.employee_id, e.last_name, e.job_id, e.department_id
  15. FROM employees e
  16. WHERE EXISTS (
  17. 	SELECT *
  18. 	FROM employees m
  19. 	WHERE e.`employee_id` = m.manager_id
  20. 	);

2、NOT EXISTS

  1. #题目：查询departments表中，不存在于employees表中的部门的department_id和department_name
  2. #方式1
  3. SELECT d.department_id, d.department_name
  4. FROM employees e RIGHT JOIN departments d
  5. ON e.department_id = d.department_id
  6. WHERE e.department_id IS NULL;
  7. #方式2
  8. SELECT department_id, department_name
  9. FROM departments d
  10. WHERE NOT EXISTS (
  11. 		SELECT *
  12. 		FROM employees e
  13. 		WHERE e.department_id = d.department_id
  14. 		)

4.4、相关更新

使用相关子查询依据一个表中的数据更新另一个表的数据。

  1. #题目：在employees中增加一个department_name字段，数据为员工对应的部门名称
  2. # 第一步
  3. ALTER TABLE employees
  4. ADD(department_name VARCHAR2(14));
  5. # 第二步
  6. UPDATE employees e
  7. SET department_name =  (SELECT department_name 
  8. 	                       FROM   departments d
  9. 	                       WHERE  e.department_id = d.department_id);

4.5、相关删除

使用相关子查询依据一个表中的数据删除另一个表的数据。

  1. #删除表employees中，其与emp_history表皆有的数据
  2. DELETE FROM employees e
  3. WHERE employee_id IN  
  4.            (SELECT employee_id
  5.             FROM   emp_history 
  6.             WHERE  employee_id = e.employee_id);

5、关于自连接和子查询效率问题

题目中可以使用子查询，也可以使用自连接。一般情况建议你使用自连接，因为在许多 DBMS 的处理过程中，对于自连接的处理速度要比子查询快得多。

可以这样理解：子查询实际上是通过未知表进行查询后的条件判断，而自连接是通过已知的自身数据表进行条件判断，因此在大部分 DBMS 中都对自连接处理进行了优化。

6、练习

  1. #1.查询和Zlotkey相同部门的员工姓名和工资 
  2. SELECT last_name, salary
  3. FROM employees
  4. WHERE department_id  (
  5. 		SELECT department_id
  6. 		FROM employees
  7. 		WHERE last_name = 'Zlotkey'
  8. 		);
  9.  
  10. #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。 
  11. SELECT employee_id, last_name, salary
  12. FROM employees
  13. WHERE salary > (
  14. 		SELECT AVG(salary)
  15. 		FROM employees
  16. 		);
  17.  
  18. #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 
  19. SELECT last_name , job_id, salary
  20. FROM employees
  21. WHERE salary > ALL(
  22. 		SELECT salary
  23. 		FROM employees
  24. 		WHERE job_id = 'SA_MAN'
  25. 		);
  26.  
  27. #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 
  28. SELECT employee_id, last_name
  29. FROM employees
  30. WHERE department_id IN(
  31. 		SELECT DISTINCT department_id
  32. 		FROM employees
  33. 		WHERE last_name LIKE '%u%'
  34. 		);
  35.  
  36.  
  37. #5.查询在部门的location_id为1700的部门工作的员工的员工号 
  38. SELECT employee_id
  39. FROM employees
  40. WHERE department_id IN(
  41. 		SELECT department_id
  42. 		FROM `departments`
  43. 		WHERE `location_id` = 1700
  44. 		);
  45.  
  46. #6.查询管理者是King的员工姓名和工资
  47. #方法1
  48. SELECT last_name, salary
  49. FROM employees
  50. WHERE manager_id IN(
  51. 		SELECT employee_id
  52. 		FROM employees
  53. 		WHERE last_name = 'King'
  54. 		);
  55.  
  56. #7.查询工资最低的员工信息: last_name, salary 
  57. SELECT last_name, salary
  58. FROM employees
  59. WHERE salary = (
  60. 		SELECT MIN(salary)
  61. 		FROM employees
  62. 		);
  63.  
  64. #8.查询平均工资最低的部门信息
  65. #方式1
  66. SELECT *
  67. FROM departments
  68. WHERE department_id = (
  69. 		SELECT department_id
  70. 		FROM employees
  71. 		GROUP BY department_id
  72. 		HAVING AVG(salary) = (
  73. 					SELECT MIN(avg_sal)
  74. 					FROM (
  75. 						SELECT AVG(salary) avg_sal
  76. 						FROM employees
  77. 						GROUP BY department_id
  78. 						) t_dept_avg_sal
  79. 					)
  80. 		);
  81. #方式2
  82. SELECT *
  83. FROM departments
  84. WHERE department_id = (
  85. 		SELECT department_id
  86. 		FROM employees
  87. 		GROUP BY department_id
  88. 		HAVING AVG(salary) <= ALL(
  89. 					SELECT AVG(salary)
  90. 					FROM employees
  91. 					GROUP BY department_id
  92. 					)
  93. 		);
  94. #方式3:LIMIT
  95. SELECT *
  96. FROM departments
  97. WHERE department_id = (
  98. 		SELECT department_id
  99. 		FROM employees
  100. 		GROUP BY department_id
  101. 		HAVING AVG(salary) = (
  102. 					SELECT AVG(salary) avg_sal
  103. 					FROM employees
  104. 					GROUP BY department_id
  105. 					ORDER BY avg_sal ASC
  106. 					LIMIT 0,1
  107. 					)
  108. 			)
  109. #方式4
  110. SELECT d.*
  111. FROM departments d, (
  112. 		SELECT department_id, AVG(salary) avg_sal
  113. 		FROM employees
  114. 		GROUP BY department_id
  115. 		ORDER BY avg_sal ASC
  116. 		LIMIT 0,1
  117. 		) t_dept_avg_sal
  118. WHERE d.department_id = t_dept_avg_sal.department_id;
  119.  
  120.  
  121.  
  122. #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） 
  123. #方式1：
  124. SELECT d.*,(SELECT AVG(salary) FROM employees WHERE department_id = d.`department_id`) avg_sal
  125. FROM departments d
  126. WHERE department_id = (
  127. 			SELECT department_id
  128. 			FROM employees
  129. 			GROUP BY department_id
  130. 			HAVING AVG(salary ) = (
  131. 						SELECT MIN(avg_sal)
  132. 						FROM (
  133. 							SELECT AVG(salary) avg_sal
  134. 							FROM employees
  135. 							GROUP BY department_id
  136. 							) t_dept_avg_sal
  137.  
  138. 						)
  139. 			);
  140.  
  141. #方式2：
  142.  
  143. SELECT d.*,(SELECT AVG(salary) FROM employees WHERE department_id = d.`department_id`) avg_sal
  144. FROM departments d
  145. WHERE department_id = (
  146. 			SELECT department_id
  147. 			FROM employees
  148. 			GROUP BY department_id
  149. 			HAVING AVG(salary ) <= ALL(
  150. 						SELECT AVG(salary)
  151. 						FROM employees
  152. 						GROUP BY department_id
  153. 						)
  154. 			);
  155.  
  156. #方式3： LIMIT
  157.  
  158. SELECT d.*,(SELECT AVG(salary) FROM employees WHERE department_id = d.`department_id`) avg_sal
  159. FROM departments d
  160. WHERE department_id = (
  161. 			SELECT department_id
  162. 			FROM employees
  163. 			GROUP BY department_id
  164. 			HAVING AVG(salary ) =(
  165. 						SELECT AVG(salary) avg_sal
  166. 						FROM employees
  167. 						GROUP BY department_id
  168. 						ORDER BY avg_sal ASC
  169. 						LIMIT 1		
  170. 						)
  171. 			);
  172.  
  173. #方式4：
  174.  
  175. SELECT d.*,(SELECT AVG(salary) FROM employees WHERE department_id = d.`department_id`) avg_sal
  176. FROM departments d,(
  177. 		SELECT department_id,AVG(salary) avg_sal
  178. 		FROM employees
  179. 		GROUP BY department_id
  180. 		ORDER BY avg_sal ASC
  181. 		LIMIT 0,1
  182. 		) t_dept_avg_sal
  183. WHERE d.`department_id` = t_dept_avg_sal.department_id
  184.  
  185. #10.查询平均工资最高的 job 信息 
  186. #方式1：
  187. SELECT *
  188. FROM jobs
  189. WHERE job_id = (
  190. 		SELECT job_id
  191. 		FROM employees
  192. 		GROUP BY job_id
  193. 		HAVING AVG(salary) = (
  194. 					SELECT MAX(avg_sal)
  195. 					FROM (
  196. 						SELECT AVG(salary) avg_sal
  197. 						FROM employees
  198. 						GROUP BY job_id
  199. 						) t_job_avg_sal
  200. 					)
  201. 		);
  202. #方式2：
  203. SELECT *
  204. FROM jobs
  205. WHERE job_id = (
  206. 		SELECT job_id
  207. 		FROM employees
  208. 		GROUP BY job_id
  209. 		HAVING AVG(salary) >= ALL(
  210. 				     SELECT AVG(salary) 
  211. 				     FROM employees
  212. 				     GROUP BY job_id
  213. 				     )
  214. 		);
  215. #方式3：
  216. SELECT *
  217. FROM jobs
  218. WHERE job_id = (
  219. 		SELECT job_id
  220. 		FROM employees
  221. 		GROUP BY job_id
  222. 		HAVING AVG(salary) =(
  223. 				     SELECT AVG(salary) avg_sal
  224. 				     FROM employees
  225. 				     GROUP BY job_id
  226. 				     ORDER BY avg_sal DESC
  227. 				     LIMIT 0,1
  228. 				     )
  229. 		);
  230. #方式4：
  231. SELECT j.*
  232. FROM jobs j,(
  233. 		SELECT job_id,AVG(salary) avg_sal
  234. 		FROM employees
  235. 		GROUP BY job_id
  236. 		ORDER BY avg_sal DESC
  237. 		LIMIT 0,1		
  238. 		) t_job_avg_sal
  239. WHERE j.job_id = t_job_avg_sal.job_id
  240.  
  241. #11.查询平均工资高于公司平均工资的部门有哪些? 
  242. SELECT department_id
  243. FROM employees
  244. WHERE department_id IS NOT NULL
  245. GROUP BY department_id
  246. HAVING AVG(salary) > (
  247. 		SELECT AVG(salary)
  248. 		FROM employees
  249. 		);
  250.  
  251. #12.查询出公司中所有 manager 的详细信息 
  252. #方式1：自连接
  253. SELECT DISTINCT mgr.employee_id,mgr.last_name,mgr.job_id,mgr.department_id
  254. FROM employees emp JOIN employees mgr
  255. ON emp.manager_id = mgr.employee_id;
  256.  
  257. #方式2：子查询
  258. SELECT employee_id,last_name,job_id,department_id
  259. FROM employees
  260. WHERE employee_id IN (
  261. 			SELECT DISTINCT manager_id
  262. 			FROM employees
  263. 			);
  264. #方式3：使用EXISTS
  265. SELECT employee_id,last_name,job_id,department_id
  266. FROM employees e1
  267. WHERE EXISTS (
  268. 	       SELECT *
  269. 	       FROM employees e2
  270. 	       WHERE e1.`employee_id` = e2.`manager_id`
  271. 	     );
  272. 	     
  273. 	     
  274.  
  275. #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? 
  276. #方式1：
  277. SELECT MIN(salary)
  278. FROM employees
  279. WHERE department_id = (
  280. 			SELECT department_id
  281. 			FROM employees
  282. 			GROUP BY department_id
  283. 			HAVING MAX(salary) = (
  284. 						SELECT MIN(max_sal)
  285. 						FROM (
  286. 							SELECT MAX(salary) max_sal
  287. 							FROM employees
  288. 							GROUP BY department_id
  289. 							) t_dept_max_sal
  290. 						)
  291. 			);
  292.  
  293. SELECT *
  294. FROM employees
  295. WHERE department_id = 10;
  296. #方式2：
  297. SELECT MIN(salary)
  298. FROM employees
  299. WHERE department_id = (
  300. 			SELECT department_id
  301. 			FROM employees
  302. 			GROUP BY department_id
  303. 			HAVING MAX(salary) <= ALL (
  304. 						SELECT MAX(salary)
  305. 						FROM employees
  306. 						GROUP BY department_id
  307. 						)
  308. 			);
  309. #方式3：
  310. SELECT MIN(salary)
  311. FROM employees
  312. WHERE department_id = (
  313. 			SELECT department_id
  314. 			FROM employees
  315. 			GROUP BY department_id
  316. 			HAVING MAX(salary) = (
  317. 						SELECT MAX(salary) max_sal
  318. 						FROM employees
  319. 						GROUP BY department_id
  320. 						ORDER BY max_sal ASC
  321. 						LIMIT 0,1
  322. 						)
  323. 			);	
  324. #方式4：
  325. SELECT MIN(salary)
  326. FROM employees e,(
  327. 		SELECT department_id,MAX(salary) max_sal
  328. 		FROM employees
  329. 		GROUP BY department_id
  330. 		ORDER BY max_sal ASC
  331. 		LIMIT 0,1
  332. 		) t_dept_max_sal
  333. WHERE e.department_id = t_dept_max_sal.department_id
  334.  
  335. #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 
  336. #方式1：
  337. SELECT last_name, department_id, email, salary
  338. FROM employees
  339. WHERE employee_id IN ANY (
  340. 			SELECT DISTINCT manager_id
  341. 			FROM employees
  342. 			WHERE department_id = (
  343. 						SELECT department_id
  344. 						FROM employees
  345. 						GROUP BY department_id
  346. 						HAVING AVG(salary) = (
  347. 									SELECT MAX(avg_sal)
  348. 									FROM (
  349. 										SELECT AVG(salary) avg_sal
  350. 										FROM employees
  351. 										GROUP BY department_id
  352. 										) t_dept_avg_sal
  353. 									)
  354. 						)
  355. 			);
  356. #方式2：
  357. SELECT last_name, department_id, email, salary
  358. FROM employees
  359. WHERE employee_id = ANY (
  360. 			SELECT DISTINCT manager_id
  361. 			FROM employees
  362. 			WHERE department_id = (
  363. 						SELECT department_id
  364. 						FROM employees
  365. 						GROUP BY department_id
  366. 						HAVING AVG(salary) >= ALL (
  367. 								SELECT AVG(salary) avg_sal
  368. 								FROM employees
  369. 								GROUP BY department_id
  370. 								)
  371. 						)
  372. 			);
  373. #方式3：
  374. SELECT last_name, department_id, email, salary
  375. FROM employees
  376. WHERE employee_id IN (
  377. 			SELECT DISTINCT manager_id
  378. 			FROM employees e,(
  379. 					SELECT department_id,AVG(salary) avg_sal
  380. 					FROM employees
  381. 					GROUP BY department_id
  382. 					ORDER BY avg_sal DESC
  383. 					LIMIT 0,1
  384. 					) t_dept_avg_sal
  385. 			WHERE e.`department_id` = t_dept_avg_sal.department_id
  386. 			);
  387.  
  388. #15. 查询部门的部门号，其中不包括job_id是"ST_CLERK"的部门号 
  389. #方式1：
  390. SELECT department_id
  391. FROM departments
  392. WHERE department_id NOT IN (
  393. 			SELECT DISTINCT department_id
  394. 			FROM employees
  395. 			WHERE job_id = 'ST_CLERK'
  396. 			);
  397. #方式2：
  398. SELECT department_id
  399. FROM departments d
  400. WHERE NOT EXISTS (
  401. 		SELECT *
  402. 		FROM employees e
  403. 		WHERE d.`department_id` = e.`department_id`
  404. 		AND e.`job_id` = 'ST_CLERK'
  405. 		);
  406.  
  407.  
  408. #16. 选择所有没有管理者的员工的last_name 
  409. SELECT last_name
  410. FROM employees e
  411. WHERE NOT EXISTS (
  412. 		SELECT employee_id
  413. 		FROM employees m
  414. 		WHERE e.manager_id = m.employee_id
  415. 		);
  416.  
  417. #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' 
  418. #方式1：
  419. SELECT employee_id,last_name,hire_date,salary
  420. FROM employees
  421. WHERE manager_id IN (
  422. 		SELECT employee_id
  423. 		FROM employees
  424. 		WHERE last_name = 'De Haan'
  425. 		);
  426. #方式2：
  427. SELECT employee_id,last_name,hire_date,salary
  428. FROM employees e1
  429. WHERE EXISTS (
  430. 		SELECT *
  431. 		FROM employees e2
  432. 		WHERE e1.`manager_id` = e2.`employee_id`
  433. 		AND e2.last_name = 'De Haan'
  434. 		); 
  435.  
  436. #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）
  437. #方式1：使用相关子查询
  438. SELECT last_name,salary,department_id
  439. FROM employees e1
  440. WHERE salary > (
  441. 		SELECT AVG(salary)
  442. 		FROM employees e2
  443. 		WHERE department_id = e1.`department_id`
  444. 		);
  445. #方式2：在FROM中声明子查询
  446. SELECT e.last_name,e.salary,e.department_id
  447. FROM employees e,(
  448. 		SELECT department_id,AVG(salary) avg_sal
  449. 		FROM employees
  450. 		GROUP BY department_id) t_dept_avg_sal
  451. WHERE e.department_id = t_dept_avg_sal.department_id
  452. AND e.salary > t_dept_avg_sal.avg_sal
  453.  
  454.  
  455. #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） 
  456. #方式1
  457. SELECT department_name
  458. FROM departments d, (
  459. 		SELECT department_id, COUNT(*) num
  460. 		FROM employees
  461. 		GROUP BY department_id
  462. 		) dept_num
  463. WHERE d.department_id = dept_num.department_id
  464. AND num > 5
  465. #方式2
  466. SELECT department_name
  467. FROM departments d
  468. WHERE 5 < (
  469. 	   SELECT COUNT(*)
  470. 	   FROM employees e
  471. 	   WHERE d.department_id = e.`department_id`
  472. 	  );
  473.  
  474.  
  475. #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）
  476. SELECT country_id
  477. FROM locations l
  478. WHERE 2 < (
  479. 	   SELECT COUNT(*)
  480. 	   FROM departments d
  481. 	   WHERE l.`location_id` = d.`location_id`
  482. 	 );

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