数据库三表连接查询怎么做

1、创建三张测试表；

createtabletest_a(aidint,anamevarchar(20))

createtabletest_b(bidint,bnamevarchar(20))

createtabletest_c(aidint,bidint,valuevarchar(20))

2、三张表中分别插入数据；

insertintotest_avalues(1,'aname1')

insertintotest_bvalues(2,'bname1')

insertintotest_cvalues(1,2,'cvalue')

3、查询表中记录；

select10,a.*fromtest_aa

unionall

select20,b.*fromtest_bb

unionall

select*fromtest_cc

4、编写sql，进行三表关联；

selecta.aname,b.bname,c.value

fromtest_ccjointest_aa

 onc.aid=a.aid

jointest_bb

 onc.bid=b.bid

SELECT

main.dept_name as 部门名称,

count(*) as 在职员工数,

sum(acu_salary) as 实发工资总额

FROM

dept main

INNER JOIN emp a ON main.dept_code = a.dept_code

INNER JOIN salary b ON a.emp_id = b.emp_id

WHERE

-- 1为有效标识

main.alive_flag = '1'

AND a.alive_flag = '1'

AND b.alive_flag = '1'

AND b.`month` = '201101'

GROUP BY

a.dept_code

HAVING

count(*) >5

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