Question

SELECT CASE WHEN avg(count)>12 THEN 5
            WHEN avg(count)>8  THEN 4
            WHEN avg(count)>2  THEN 3
            WHEN avg(count)>1  THEN 2
            ELSE 1
            END,madeby
FROM (SELECT M.month,(SELECT count(*)
                     FROM Booking
                     WHERE date_trunc('month',starttime)=month
                         AND madeby=M.madeby
                     ) AS count,M.madeby
     FROM (SELECT date_trunc('month',generate_series(min(starttime),
                            current_timestamp,interval '1 month')::timestamp)
                            AS month,madeby
          FROM Booking
          GROUP BY madeby
     ) AS M
) AS BookingsPerMonth
GROUP BY madeby;

Now I need to do that computation there, I’m not questioning that. I’m guessing the problem is that it’s computing the aggregate function avg four times. The difference in times is from ~17 seconds with the CASE to ~4.5 seconds without (although I’m then lacking sufficient information)

Is there a way I can optimise this, through variable storage or something, such to bring the time closer to 4.5 seconds?

Answer 1

SELECT  
    CASE 
        WHEN avg_count > 12 THEN 5
        WHEN avg_count > 8  THEN 4
        WHEN avg_count > 2  THEN 3
        WHEN avg_count > 1  THEN 2
        ELSE 1
    END,
    madeby
FROM (
    SELECT avg(count) as avg_count, madeby
    FROM (
        SELECT 
            M.month,
            (
                SELECT count(*)
                FROM Booking
                WHERE date_trunc('month',starttime)=month AND madeby=M.madeby
            ) AS count, 
            M.madeby
        FROM (
            SELECT 
                date_trunc('month',generate_series(min(starttime),
                current_timestamp,interval '1 month')::timestamp) AS month,
                madeby
            FROM Booking
            GROUP BY madeby
        ) AS M
    ) AS BookingsPerMonth
    GROUP BY madeby
) AS Averages;