Write SQL query to solve given problem: Calculate the difference between running business in Glendale City and Mesa City.. Keep the solution inside sql tag ```sql [SQL-Query] ```
SELECT SUM(CASE WHEN city = 'Glendale' THEN 1 ELSE 0 END) - SUM(CASE WHEN city = 'Mesa' THEN 1 ELSE 0 END) AS diff FROM Business WHERE active = 'true'