问题描述
我想在几个表的每一个中选择Modifyed_at列的max()值:
select
max(a.modified_at) as a_modified_at,max(b.modified_at) as b_modified_at,max(c.modified_at) as c_modified_at
from a,b,c;
只要每个表至少有1行,它就可以正常工作。 问题是,当只有一个表具有0行时,将为所有表返回null:
null,null,null
有什么解决方案可以为具有行的表返回正确的值? PostgreSQL-10
解决方法
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+CMT: "+95258451525","20/09/18,23:50:28+08" # phone edited for privacy
This text is the SMS sent
OUTER JOIN
但可能更简单的选择是改为使用3个子查询:
select
max(a.modified_at) as a_modified_at,max(b.modified_at) as b_modified_at,max(c.modified_at) as c_modified_at
from a outer join b outer join c;