Identify if at least one row with given condition exists

Question

Employee table has ID and NAME columns. Names can be repeated. I want to find out if there is at least one row with name like \'kaushik%\'.

So query should return true/f

Answer 1

since you require that the sql query should return 1 or 0, then you can try the following query :-

select count(1) from dual 
where exists(SELECT 1 
             FROM employee
             WHERE name like 'kaushik%')

Since the above query uses Exists, then it will scan the employee table and as soon as it encounters the first record where name matches "kaushik", it will return 1 (without scanning the rest of the table). If none of the records match, then it will return 0.

Answer 2

How about:

select max(case when name like 'kraushik%' then 1 else 0 end)
from employee

Or, what might be more efficient since like can use indexes:

select count(x)
from (select 1 as x
      from employee
      where name like 'kraushik%'
     ) t
where rownum = 1

Answer 3

select 1 
 where exists ( select name 
                  from employee 
                  where name like 'kaushik%'
               )

Answer 4

Commonly, you'd express this as either

SELECT COUNT(*)
  FROM employee
 WHERE name like 'kaushik%'
   AND rownum = 1

where the rownum = 1 predicate allows Oracle to stop looking as soon as it finds the first matching row or

SELECT 1
  FROM dual
 WHERE EXISTS( SELECT 1
                 FROM employee
                WHERE name like 'kaushik%' )

where the EXISTS clause allows Oracle to stop looking as soon as it finds the first matching row.

The first approach is a bit more compact but, to my eye, the second approach is a bit more clear since you really are looking to determine whether a particular row exists rather than trying to count something. But the first approach is pretty easy to understand as well.