GROUP BY времево клеймо на всеки 15 минути, включително липсващи записи

Ако наистина искате да го направите в mysql, това трябва да работи до известна степен - в зависимост от това как искате да организирате вашите 15-минутни интервали. Дадох изхода като time from | time to | number of reports защото смятам, че е безсмислено и дори малко измамно да се изведе конкретна времева марка и да се свърже отброяване на времеви диапазон с него.

SELECT CONCAT (
        lpad(hours.a, 2, "0"),
        ":",
        lpad(minutes.a * 15, 2, "0"),
        ":00"
        ) AS 'from',
    CONCAT (
        lpad(hours.a, 2, "0"),
        ":",
        lpad((minutes.a * 15) + 14, 2, "0"),
        ":59"
        ) AS 'to',
    count(r.id)
FROM (
    SELECT 0 AS a

    UNION

    SELECT 1 AS a

    UNION

    SELECT 2 AS a

    UNION

    SELECT 3 AS a

    UNION

    SELECT 4 AS a

    UNION

    SELECT 5 AS a

    UNION

    SELECT 6 AS a

    UNION

    SELECT 7 AS a

    UNION

    SELECT 8 AS a

    UNION

    SELECT 9 AS a

    UNION

    SELECT 10 AS a

    UNION

    SELECT 11 AS a

    UNION

    SELECT 12 AS a

    UNION

    SELECT 13 AS a

    UNION

    SELECT 14 AS a

    UNION

    SELECT 15 AS a

    UNION

    SELECT 16 AS a

    UNION

    SELECT 17 AS a

    UNION

    SELECT 18 AS a

    UNION

    SELECT 19 AS a

    UNION

    SELECT 20 AS a

    UNION

    SELECT 21 AS a

    UNION

    SELECT 22 AS a

    UNION

    SELECT 23 AS a
    ) hours
INNER JOIN (
    SELECT 0 AS a

    UNION

    SELECT 1 AS a

    UNION

    SELECT 2 AS a

    UNION

    SELECT 3 AS a
    ) minutes
LEFT JOIN reports r ON hours.a = hour(r.t)
    AND minutes.a = floor(minute(r.t) / 15)
GROUP BY hours.a,
    minutes.a;