Join Two Select Statements With Different Columns And Condition

Question

I'm not good at asking question, so i'll give an example of what i want to have.

if i = 1 and xi = 0 then
    select a,b,c,d,e,f,g where z = 1
elseif i=0 and xi = 1 then
    select a,c,f,h,l,n where w = var
elseif i=1 and xi=1 then
    select a,b,c,d,e,f,g, where z = 1
    union all
    select a,c,f,h,l,n where w = var
end if

How can I join the 2 select statement if their columns are not equal and they both have a unique condition?

Answer 1

Based on the conditions you can create derived tables to fetch desired columns and then to get a union of the two tables add null values in column list of derived tables which have less number of columns:

Pseudo code:

select * from 
(select a,b,c,d,e,f,g
 where  z = 1 
 and 1 = case when i = 1 and xi = 0 then 1 
             when i = 1 and xi = 1 then 1
             else 0 
        end) as T1
 union all             
(select a,c,f,h,l,n ,null -- add null value to equate number of columns
where w = var 
and 1 = case when i=0 and xi = 1 then 1 
             when i=1 and xi = 1 then 1
             else 0 
        end) as T2

Hope this helps!!!

Answer 2

If it is not a requirement not to use dynamic sql I will opt for that one.

Another idea will be to use user defined function returnin tables.

So you encapsulate there the logic...