Select + count разных параметров

Нужно использовать CASE внутри COUNT

SELECT
   Site_id,
   COUNT(CASE Level WHEN 0 THEN 1 END) AS Level_0,
   COUNT(CASE Level WHEN 1 THEN 1 END) AS Level_1
FROM Table
GROUP BY Site_id;

SELECT
   Site_id,
   SUM(Level = 0) AS Level_0,
   SUM(Level = 1) AS Level_1
FROM DataTable
GROUP BY Site_id;