SQL to update the salary of employees with their department's average salary

问题

Consider the table employee:

desc employee;

Name                       Null?    Type
-------------------------- -------- ------------
EMPLOYEENO                 NOT NULL NUMBER(4)
ENAME                               VARCHAR2(15)
JOB                                 VARCHAR2(15)
MGR                                 NUMBER(4)
HIREDATE                            DATE
SAL                                 NUMBER
COMM                                NUMBER
DEPTNO                              NUMBER(2)

Contains with values of deptno,sal as:

    DEPTNO      SAL
---------- ----------
        10     2450
        10     5000
        10     1300
        20     2975
        20     3000
        20     1100
        20      800
        20     3000
        30     1250
        30     1500
        30     1600
        30      950
        30     2850
        30     1250

Need to update the salary of employees with their department's average salary. i.e set every employee's salary to the departmental average.Is there any solution possible with the group by clause something like

update employee set sal =(select avg(sal) from employee group by deptno) where deptno in(select deptno from employee group by deptno)

So how to query the same.

回答1:

Try this

UPDATE EMPLOYEE A
SET SAL = (SELECT AVG(SAL) FROM EMPLOYEE B WHERE B.DEPTNO = A.DEPTNO);

回答2:

update employee a
set sal =  (select avg(sal) as avgsal
          from employee b
          where A.DEPTNO = b.deptno
        );

回答3:

This would be much more efficiently implemented as a MERGE, in which the USING clause aggregates salaries for all departments to the department level and joins to the employee table on department_id.

来源：https://stackoverflow.com/questions/14544971/sql-to-update-the-salary-of-employees-with-their-departments-average-salary