Question

I have a situation where I would require to do a conditional join based on the value of the columns on one of the tables.


table_a ta

    join table_b tb on

    case

     when ta.column_1 = 1 then ta.column_2 = tb.column_2

     when ta.column_1 = 2 then ta.column_2 = tb.column_2 and ta.column_3 = tb.column_3

     when ta.column_1 = 3 then ta.column_2 = tb.column_2 and ta.column_3 = tb.column_3 and ta.column_4 = tb.column_4

    end


Please advise how I should go about it?

Tried searching and got some options to use a left join but I am not sure how to do it. 🙁

Please advise.

Answer 1

i think it’s all can be formulated as single boelean expression

...
join table_b tb on 
(ta.column_1 = 1 and ta.column_2 = tb.column_2) or
(ta.column_1 = 2 and ta.column_2 = tb.column_2 and ta.column_3 = tb.column_3)
...