表 a
aid avendor av_vendor aMAT
1 VT001 VT10 Y2B
2 SC002 SC20 Y1B
3 PV001 PV10 Y2B
4 VT001 VT11 Y2B
5 VT001 VT11 Y2B
6 ST001 ST01 Y2B
……
表 b
bid b_vendor bv_vendor b_MAT
1 VT011 VT11 Y2B
2 SC022 SC02 Y1B
3 PV011 PV01 Y2B
4 VT021 VT21 Y2B
5 VT021 VT21 Y2B
6 ST001 ST01 Y2C
……
现要求得到以下数据
vendor v_vendor MAT
VT001 VT10 Y2B
PV001 PV10 Y2B
VT001 VT11 Y2B
ST001 ST01 Y2B
PV011 PV01 Y2B
VT021 VT21 Y2B
……
即 要得到 表a与 表b 中 aMAT 等于 Y2B ，bMAT 等于 Y2B
的值
------解决方案--------------------
select avendor,av_vendor,aMAT from a where aMAT='Y2B'
union all
select b_vendor,bv_vendor,b_MAT from b where b_MAT='Y2B'
要是想去重的话就去掉all关键字
------解决方案--------------------
select avendor as vendor, av_vendor as v_vendor from a where aMAT='Y2B' union all
select bvendor as vendor, bv_vendor as v_vendor from b where bMAT='Y2B'