Question

here my query-

SELECT final.* into #FinalTemp from
    (   
    select * from #temp1 
        UNION 
    select * from #temp2 
        UNION 
    select * from #temp3 
        UNION 
    select * from #temp4
)final

but at a time only one temp table exists so how to check if #temp exists then do union or ignore?

Answer 1

You can’t have a union or query on a non-existent object at compile time (compiling to a query plan just before execution).

So there is no way to refer to a non-existent table in the same batch

The pattern you have to use is like this: dynamic SQL is a separate batch

IF OBJECT('tempdb..#temp1') IS NOT NULL
  EXEC ('SELECT * FROM #temp1')
ELSE IF OBJECT('tempdb..#temp3') IS NOT NULL
  EXEC ('SELECT * FROM #temp3')
ELSE IF OBJECT('tempdb..#temp3') IS NOT NULL
  EXEC ('SELECT * FROM #temp3')
...