 <p>This might not give the same performance as an UNION but I think this is what you are looking for</p> <p>You need to create a view:</p> <pre><code>create view mutex as select i from (select 0 union select 1)sq (i) </code></pre> <p>Now you can use this view to get your desired results as:</p> <pre><code>select coalesce(a.A,b.B),coalesce(a.coll1,b.coll1),coalesce(a.coll2,b.coll2),coalesce(a.coll3,b.coll3) from mutex left join TABLE_A as a on i =0 left join TABLE_B as b on i =1 </code></pre> <p>Note: Instead of a mutex view, you can also use a table that will have these 2 rows</p>