为什么left join 的执行结果右表会结果会填入所有行

Question

我用了一个left join的查询语句，左表符合条件的有15条，右表只有一条，但是查询出来的结果并没有像说明里面那样右表不符合的为空

左表语句：select *from Embryo_UsingTab where ProcessNum = '2205130946_CTH870PT220308295'

右表语句：select*from Embryo_Message where ProcessNum = '2205130946_CTH870PT220308295'

联合查询
select ManufacturedNum,EntryNum,RemainNum,b.EmbryoNum,status from Embryo_UsingTab a
left outer join Embryo_Message b
on a.ProcessNum = b.processNum where a.ProcessNum = '2205130946_CTH870PT220308295'

Answer 1