1、错误SQL ：

select o.PK_ORG,o.NAME_TC,o.FK_ORG

from dbo.org o

left join dbo.ORGDUTY od on o.PK_ORG =od.FK_ORG and o.FK_SRCMAIN =od.FK_SRCMAIN

where od.FK_DUTY =1  and o.fk_srcmain=2021

此时，Where 子句中错误放置 " od.FK_DUTY=1 " 会过滤掉 dbo.ORGDUTY 不存在资料的 dbo.ORG，

         即把Left Join 该有的作用给抵消了。

 

2、正确SQL ：

select o.PK_ORG,o.NAME_TC,o.FK_ORG

from dbo.org o

left join dbo.ORGDUTY od on o.PK_ORG =od.FK_ORG and o.FK_SRCMAIN =od.FK_SRCMAIN and od.FK_DUTY =1

where o.fk_srcmain=2021