Question

I want to Join multiple tables using IF ELSE statement within Sql Query when column value match with the specified text.

Suppose I have checked coloumnName='Value' Then I want to JOIN an additional Table; otherwise, I do not want to join it. Is this possible? How can I do that?

Answer 1

You cannot conditionally join a table You need to join all tables unconditionally using an outer join, use the condition in the join criteria, and pick the values that you want from the returned data set, like this:

select r.id, p.name, a.name, t.name
from requests r
left outer join person p on r.type='person' and r.item_id = p.id
left outer join animal a on r.type='animal' and r.item_id = a.id
left outer join thing t on r.type='thing' and r.item_id = t.id

The example above shows “requests” that have an item_id that references a person, an animal, or a thing. The type column decides which table is referenced.

The result will have three columns for name, at most one of which will be non-null.