union all 与 union 去重
union all与union的区别:
union all对结果集不会去除重复的结果,union会去除重复的结果
select distinct HZDDH,HTBH,HTSX,XSYMC,b.PH,b.YS from XSHTMLH h left join XSHTMLB b on h.djlsh=b.djlsh
union all
select distinct HZDDH,HTBH,ddlx as HTSX,YWY as XSYMC,b.PH,b.ys from CPCJDDH h left join CPCJDDB b on h.djlsh=b.djlsh
等价于
select HZDDH,HTBH,HTSX,XSYMC,b.PH,b.YS from XSHTMLH h left join XSHTMLB b on h.djlsh=b.djlsh
union
select HZDDH,HTBH,ddlx as HTSX,YWY as XSYMC,b.PH,b.ys from CPCJDDH h left join CPCJDDB b on h.djlsh=b.djlsh
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