11-高级子查询
1 --子查询
2 --子查询 (内查询) 在主查询执行之前执行
3 --主查询(外查询)使用子查询的结果
4 --问题：查询工资大于149号员工工资的员工的信息
5 SELECT last_name
6 FROM employees
7 WHERE salary >
8 (SELECT salary
9 FROM employees
10 WHERE employee_id = 149) ;
11
12 --多利子查询
13 --主查询与子查询返回的多个列进行比较
14 --主查询与子查询返回的多个列进行比较
15 --多列子查询中的比较分为两种:
16 --成对比较
17 --不成对比较
18
19 --成对比较举例
20 --问题：查询与141号或174号员工的manager_id和department_id相同的其他员工的employee_id, manager_id, department_id
21 SELECT employee_id, manager_id, department_id
22 FROM employees
23 WHERE (manager_id, department_id) IN
24 (SELECT manager_id, department_id
25 FROM employees
26 WHERE employee_id IN (141,174))
27 AND employee_id NOT IN (141,174);
28
29 --不成对比较举例
30 SELECT employee_id, manager_id, department_id
31 FROM employees
32 WHERE manager_id IN (SELECT manager_id
33 FROM employees
34 WHERE employee_id IN (174,141))
35 AND department_id IN (SELECT department_id
36 FROM employees
37 WHERE employee_id IN (174,141))
38 AND employee_id NOT IN(174,141);
39
40 --在 FROM 子句中使用子查询
41 --问题：返回比本部门平均工资高的员工的last_name, department_id, salary及平均工资
42 --方法一
43 select last_name,department_id,salary,
44 (select avg(salary)from employees e3
45 where e1.department_id = e3.department_id
46 group by department_id) avg_salary
47 from employees e1
48 where salary >
49 (select avg(salary)
50 from employees e2
51 where e1.department_id = e2.department_id
52 group by department_id
53 )
54
55 --方法二
56 SELECT a.last_name, a.salary,
57 a.department_id, b.salavg
58 FROM employees a, (SELECT department_id,
59 AVG(salary) salavg
60 FROM employees
61 GROUP BY department_id) b
62 WHERE a.department_id = b.department_id
63 AND a.salary > b.salavg;
64
65 --单列子查询表达式
66 --单列子查询表达式是在一行中只返回一列的子查询
67 --Oracle8i 只在下列情况下可以使用, 例如:
68 -- SELECT 语句 (FROM 和 WHERE 子句)
69 -- INSERT 语句中的VALUES列表中
70 --Oracle9i中单列子查询表达式可在下列情况下使用:
71 -- DECODE 和 CASE
72 -- SELECT 中除 GROUP BY 子句以外的所有子句中
73
74 --在 CASE 表达式中使用单列子查询
75 --问题：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’。
76 SELECT employee_id, last_name,
77 (CASE
78 WHEN department_id =(SELECT department_id FROM departments WHERE location_id = 1800)
79 THEN 'Canada' ELSE 'USA' END) location
80 FROM employees;
81
82 --在 ORDER BY 子句中使用单列子查询
83 --问题：查询员工的employee_id,last_name,要求按照员工的department_name排序
84 SELECT employee_id, last_name
85 FROM employees e
86 ORDER BY (SELECT department_name
87 FROM departments d
88 WHERE e.department_id = d.department_id);
89
90 --相关子查询
91 --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
92 --问题：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
93 SELECT last_name, salary, department_id
94 FROM employees outer
95 WHERE salary >(SELECT AVG(salary)
96 FROM employees
97 WHERE department_id = outer.department_id) ;
98
99 --问题：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
100 SELECT e.employee_id, last_name,e.job_id
101 FROM employees e
102 WHERE 2 <= (SELECT COUNT(*)
103 FROM job_history
104 WHERE employee_id = e.employee_id);
105
106 --EXISTS 操作符
107 --EXISTS 操作符检查在子查询中是否存在满足条件的行
108 --如果在子查询中存在满足条件的行:
109 -- 不在子查询中继续查找
110 -- 条件返回 TRUE
111 --如果在子查询中不存在满足条件的行:
112 -- 条件返回 FALSE
113 -- 继续在子查询中查找
114 --问题：查询公司管理者的employee_id,last_name,job_id,department_id信息
115 SELECT employee_id, last_name, job_id, department_id
116 FROM employees outer
117 WHERE EXISTS ( SELECT 'X'
118 FROM employees
119 WHERE manager_id =
120 outer.employee_id);
121
122 --NOT EXISTS 操作符应用举例
123 --问题：查询departments表中，不存在于employees表中的部门的department_id和department_name
124 SELECT department_id, department_name
125 FROM departments d
126 WHERE NOT EXISTS (SELECT 'X'
127 FROM employees
128 WHERE department_id
129 = d.department_id);
130
131 --相关更新
132 --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
133 --eg:1
134 ALTER TABLE employees
135 ADD(department_name VARCHAR2(14));
136 --eg:2
137 UPDATE employees e
138 SET department_name =
139 (SELECT department_name
140 FROM departments d
141 WHERE e.department_id = d.department_id);
142
143 --相关删除
144 --问题：删除表employees中，其与emp_history表皆有的数据
145 DELETE FROM employees E
146 WHERE employee_id =
147 (SELECT employee_id
148 FROM emp_history
149 WHERE employee_id = E.employee_id);
150
151 --WITH 子句
152 --使用 WITH 子句, 可以避免在 SELECT 语句中重复书写相同的语句块
153 --WITH 子句将该子句中的语句块执行一次并存储到用户的临时表空间中
154 --使用 WITH 子句可以提高查询效率
155 --问题：查询公司中各部门的总工资大于公司中各部门的平均总工资的部门信息
156 WITH
157 dept_costs AS (
158 SELECT d.department_name, SUM(e.salary) AS dept_total
159 FROM employees e, departments d
160 WHERE e.department_id = d.department_id
161 GROUP BY d.department_name),
162 avg_cost AS (
163 SELECT SUM(dept_total)/COUNT(*) AS dept_avg
164 FROM dept_costs)
165 SELECT *
166 FROM dept_costs
167 WHERE dept_total >
168 (SELECT dept_avg
169 FROM avg_cost)
170 ORDER BY department_name;
eg：
1 --查询员工的last_name, department_id, salary.其中员工的salary,department_id与有奖金的任何一个员工的salary,department_id相同即可
2 select last_name, department_id, salary
3 from employees
4 where (salary,department_id) in (
5 select salary,department_id
6 from employees
7 where commission_pct is not null
8 );
9
10 --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
11 select last_name, job_id, salary
12 from employees
13 where salary > all(
14 select salary
15 from employees
16 where job_id = 'SA_MAN'
17 );
18
19 --选择所有没有管理者的员工的last_name
20 select last_name
21 from employees e1
22 where not exists (
23 select 'A'
24 from employees e2
25 where e1.manager_id = e2.employee_id
26 );
