Question

I have 3 tables – TableA, TableB and TableDetail

**Table Detail**
id  FinalValue
1       99
2       88
3       77


**Table A**
id   InitValue   Num
1     10         100
2     30         200


**Table B**
id   InitValue  Num
3    20          200

My requirement is to get the FinalValue from TableDetail based on

Num 

(Num value will be selected by user from a textBox UI).If TableB has a record for the partcular Num, then use Table B’s id.If not, then use Table A’s id.
The assumption is that Table A has records for all Num values.

For example,

If Num=200:

Since a record exists in TableB for Num=200, use TableB’s corresponding id (3) and get FinalValue from TableDetail where id=3, i.e.

FinalValue = 77

If Num =100:

SinceTableB does not have any record for Num=100,use TableA’s corresponding id (1) and get FinalValue from TableDetail where id=1, i.e.

FinalValue = 99

Can you plese help me frame a PL/SQL query for the same.Thanks!

Answer 1

try the following, @num is passed by user

select FinalValue
from TableDetail
where id in
(select isnull(T2.id,T1.id)
from TableA T1 on T.id = T1.id and T1.Num = @num
left join TableB T2 on T.id = T2.id and T2.Num = @num)