multiple select query for the same tables with union
I'm not entirely clear on what you are trying to do, how should the top 4 in each category be chosen for example, randomly?

WITH PRIMARY_CHOICE AS (
  SELECT ApplicantName, Category, Plus2Percentage
  FROM (
    SELECT ApplicantName, Category, Plus2Percentage
         , row_number() over (partition by Category
                              order by Plus2Percentage desc) as rn
    FROM RKMVApplicationFormData
  ) as T 
  WHERE rn &lt;= CASE CATEGORY WHEN 'SC' THEN 25
                            WHEN 'ST' THEN 30
                            WHEN 'OBC' THEn 15
                            ELSE 0
              END
)
SELECT ApplicantName, Category, Plus2Percentage
FROM PRIMARY_CHOICE
UNION ALL
SELECT ApplicantName, Category, Plus2Percentage
FROM (
    SELECT ApplicantName, Category, Plus2Percentage
         , row_number() over (order by Plus2Percentage desc) as rn
    FROM RKMVApplicationFormData x
    WHERE NOT EXISTS (
        select 1 from primary_choice y
        where x.ApplicantName = y.ApplicantName
    )
) AS T2
WHERE rn &lt;= 30;