Question

Query 1:

SELECT if(COUNT(0),1,0) as 'IsPresent'
FROM table1
WHERE Id=1500;    

Query2:

If IsPresent is 1, then

select t2.mark,t2.age from table2  t2,table1 t1
where  t1.ID=t2.ID order by t1.ID;

If IsPresent is 0, then

select mark,age from table2;

ie. if entry is present in a table, i need to join else i don’t need to join.

Is there any way we can achieve this with a single mysql select query?

Answer 1

I think you can union the two different query cases which would look like:

SELECT T2.MARK, T2.AGE
FROM TABLE1 T1, TABLE2 T2
WHERE
  T1.ID=T2.ID AND
  T1.ID=1500
UNION
SELECT MARK, AGE
FROM TABLE1
WHERE
  NOT ID=1500