1 #1.查詢工資最低的員工資訊：last name, salary
  2 SELECT
  3     last_name,
  4     salary
  5 FROM
  6     employees
  7 WHERE
  8     salary = (
  9         SELECT
 10             MIN(salary)
 11         FROM
 12             employees
 13     );
 14 
 15 #2.查詢平均工資最低的部門資訊
 16 SELECT
 17     *
 18 FROM
 19     departments
 
 20 WHERE
 21     department_id = (
 22         SELECT
 23             department_id
 24         FROM
 25             employees
 26         GROUP BY
 27             department_id
 28         ORDER BY
 29             avg(salary)
 30         LIMIT 1
 31     );
 32 
 33 #3.查詢平均工資最低的部門資訊和該部門的平均工資
 34 #①各部門的平均工資
 
 35 SELECT
 36     avg(salary),
 37     department_id
 38 FROM
 39     employees
 40 GROUP BY
 41     department_id #②求出最低平均工資的部門編號
 42     SELECT
 43         avg(salary),
 44         department_id
 45     FROM
 46         employees
 47     GROUP BY
 48         department_id
 49     ORDER BY
 50         avg
 
(salary)
 51     LIMIT 1;
 52 
 53 #③查詢部門資訊
 54 SELECT
 55     d.*, ag
 56 FROM
 57     departments d
 58 JOIN (
 59     SELECT
 60         avg(salary),
 61         department_id
 62     FROM
 63         employees
 64     GROUP BY
 65         department_id
 66     ORDER BY
 67         avg(salary)
 68     LIMIT 1
 69 ) ag_dep ON d.department_id = ag_dep.department_id #4.查詢平均工資最高的job資訊
 70 SELECT
 71     avg(salary)
 72 FROM
 73     employees
 74 GROUP BY
 75     job_id
 76 ORDER BY
 77     avg(salary) DESC
 78 LIMIT 1 ②查詢job資訊 SELECT
 79     *
 80 FROM
 81     jobs
 82 WHERE
 83     job_id = (
 84         SELECT
 85             job_id
 86         FROM
 87             employees
 88         GROUP BY
 89             job_id
 90         ORDER BY
 91             avg(salary) DESC
 92         LIMIT 1
 93     );
 94 
 95 #5.查詢平均工資高於公司平均工資的部門有哪些？
 96 SELECT
 97     avg(salary),
 98     department_id
 99 FROM
100     employees
101 GROUP BY
102     department_id;
103 
104 
105 HAVING
106     avg(salary) > (
107         SELECT
108             avg(salary)
109         FROM
110             employees
111     );
112 
113 #6.查詢出公司中所有 manager的詳細資訊
114 SELECT
115     *
116 FROM
117     employees
118 WHERE
119     employee_id IN (
120         SELECT DISTINCT
121             manager_id
122         FROM
123             employees
124     );
125 
126 #7.各個部門中最高工資中最低的那個部門的最低工資是多少
127 SELECT
128     min(salary),
129     department_id
130 FROM
131     employees
132 WHERE
133     department_id = (
134         SELECT
135             department_id
136         FROM
137             employees
138         GROUP BY
139             department_id
140         ORDER BY
141             max(salary)
142         LIMIT 1
143     );
144 
145 #8.查詢平均工資最高的部門的 manager的詳細資訊：last_name, department id, email
146 SELECT
147     last_name,
148     d.department_id,
149     email,
150     salary
151 FROM
152     employees e
153 JOIN departments d ON d.manager_id = e.manager_id
154 WHERE
155     d.department_id = (
156         SELECT
157             department_id
158         FROM
159             employees
160         GROUP BY
161             department_id
162         ORDER BY
163             avg(salary) DESC
164         LIMIT 1
165     );