请教关于外连接的查询语句
这样一句查询:
select *
from dlcmb LEFT OUTER JOIN dlc ON dlcmb.lclxdm+dlcmb.lch=dlc.lclxdm+dlc.lch
where dlcmb.xslbdm='11' and dlcmb.lclxdm='20' and dlcmb.jbdm='2007' and dlc.xh='2007110075'表dlcmb附加 dlcmb.xslbdm='11' and dlcmb.lclxdm='20' and dlcmb.jbdm='2007'条件后有四条记录,
表dlc附加 dlc.xh='2007110075'后有三条记录我用来外连接,为什么还是显示三条记录,请问错在哪里?谢谢
这样一句查询:
select *
from dlcmb LEFT OUTER JOIN dlc ON dlcmb.lclxdm+dlcmb.lch=dlc.lclxdm+dlc.lch
where dlcmb.xslbdm='11' and dlcmb.lclxdm='20' and dlcmb.jbdm='2007' and dlc.xh='2007110075'表dlcmb附加 dlcmb.xslbdm='11' and dlcmb.lclxdm='20' and dlcmb.jbdm='2007'条件后有四条记录,
表dlc附加 dlc.xh='2007110075'后有三条记录我用来外连接,为什么还是显示三条记录,请问错在哪里?谢谢
from
dlcmb
LEFT OUTER JOIN
dlc ON dlcmb.lclxdm =dlc.lclxdm and dlcmb.lch=dlc.lch
from
dlcmb
LEFT OUTER JOIN
dlc ON dlcmb.lclxdm =dlc.lclxdm and dlcmb.lch=dlc.lch
*
from
dlcmb
LEFT OUTER JOIN
dlc ON dlcmb.lclxdm=dlc.lclxdm AND dlcmb.lch=dlc.lch
where
dlcmb.xslbdm='11' and dlcmb.lclxdm='20' and dlcmb.jbdm='2007' and dlc.xh='2007110075'
所以当加入第二个条件后,符合条件的记录只有三条,也就是说参与left outer运算的记录只有三条
select *
from dlcmb LEFT OUTER JOIN (select * from dlc where xh='2007110075') b ON dlcmb.lclxdm+dlcmb.lch=b.lclxdm+b.lch
where dlcmb.xslbdm='11' and dlcmb.lclxdm='20' and dlcmb.jbdm='2007' 谢谢各位