oracle 子查询例题综合.doc
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1 子查询，把一个查询结果当做一张表然后对这张表进行查询或者把它看做查询条件来查询
SELECT select_list
FROM table
WHERE expr operator
(SELECT select_list
FROM table);
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使用 (外查询)
查询工资比Abel高的员工
SELECT last_name
FROM employees
WHERE salary
(SELECT salary
FROM employees
WHERE last_name = Abel);//看成一张表
查询工资最低的员工
select * from employees
where salary=(
select MIN(salary) from employees
);
查询和149号员工同一部门的其他员工
select * from employees
where department_id=(
select department_id from employees where employee_id=149)
and employee_id149
查询比202员工的部门经理工资还要高的员工
select manager_id
from departments
where department_id=(
select department_id from employees where employee_id=202
)
子查询注意事项
子查询要包含在括号内。
将子查询放在比较条件的右侧。
除非进行Top-N 分析，否则不要在子查询中使用ORDER BY 子句。
单行操作符对应单行子查询，多行操作符对应多行子查询。
2 单行子查询
只返回一行。
使用单行比较操作符。
多行子查询必须用in 单行查询可以= 可以用in
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);
在子查询中使用组函数
SELECT last_name, job_id, salary
FROM employees
WHERE salary =
(SELECT MIN(salary)
FROM employees);
查询员工编号，姓名，工资，工资总和
select employee_id,last_name,salary,(select SUM(salary) from employees) as 工资总和
from employees
首先执行子查询。
向主查询中的HAVING 子句返回结果
SELECT department_id, MIN(salary)
FROM employees
GROUP BY department_id
HAVING MIN(salary)
(SELECT MIN(salary)
FROM employees
WHERE department_id = 50);
多行子查询使用单行比较符 gropu不对
SELECT employee_id, last_name
FROM employees
WHERE salary =
(SELECT MIN(salary)
FROM employees
GROUP BY department_id);
子查询中的空值问题
子查询不返回任何行
SELECT last_name, job_id
FROM employees
WHERE job_id =
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