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