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SQL基础--子查询相关

2016-11-25 20:46 966 查看

SQL基础–子查询相关

通过子查询结果可把子查询分为以下几类：查值、查集合、查表

查值–子查询

查询员工部门名称

--查询结果作为返回字段
SELECT e.EMPLOYEE_ID,
e.LAST_NAME,
(SELECT d.DEPARTMENT_NAME
FROM DEPARTMENTS d
WHERE d.DEPARTMENT_ID = e.DEPARTMENT_ID) "DEPAT_NAME"
FROM EMPLOYEES e;

查询部门名称是“Purchasing”的员工

--查询结果做为比较条件

SELECT e.EMPLOYEE_ID,
e.LAST_NAME,
e.DEPARTMENT_ID
FROM　EMPLOYEES e
WHERE e.DEPARTMENT_ID = (
SELECT d.DEPARTMENT_ID
FROM DEPARTMENTS d
WHERE d.DEPARTMENT_NAME = 'Purchasing'
);

查集合–子查询

查询部门ID大于80的员工

--查集合子查询

SELECT e.EMPLOYEE_ID,
e.LAST_NAME,
e.DEPARTMENT_ID
FROM　EMPLOYEES e
WHERE e.DEPARTMENT_ID IN (
SELECT d.DEPARTMENT_ID
FROM DEPARTMENTS d
WHERE d.DEPARTMENT_ID > 80
);

查表–子查询

查询部门工资最大工资

--查表子查询
SELECT d.DEPARTMENT_ID,d.DEPARTMENT_NAME,MAX_SAL
FROM DEPARTMENTS d,
(SELECT DEPARTMENT_ID,MAX(SALARY) "MAX_SAL"
FROM EMPLOYEES
GROUP BY DEPARTMENT_ID) s
WHERE
s.DEPARTMENT_ID(+) = d.DEPARTMENT_ID;

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