[Database]使用 Informix Case Statement in Where Clause (Use Informix Case Statement in Where Clause)

問題

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使用 Informix Case Statement in Where Clause



解決方法

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Schema:
a table schema [id] , [b_id] , [b_ver](can be null)
b table schema [id] , [ver] , [description]

Condition:
if a.ver is null then don't join b.ver else join b.ver to get description

Answer:
select *
from a,b
where 1=1
and a.b_id=b.id
and
(case when (a.b_ver is not null)
            then  a.b_ver
else b.ver
end)
=b.ver

How to do it:
use case statement when [a.b_ver] is null then that condition become [b.ver] self,otherwise that [a.b_ver] join [b.ver]