Run a query based on output of another query

Question

I have 3 queries based on first result i have to execute the 2 or 3rd query

If the output is 2 i have to eexute 2nd query

If the op is 3 then 3rd query

pls help

Answer 1

SELECT   XX,  
     CASE 
     WHEN Y =  1 THEN (Select X from table2 where xx= )
     WHEN Y = 2 THEN  (Select X from table3 where xx=)
  END 
   FROM table1

Hope this answers your question