sql - How to fill date gaps in MySQL?

Question

How i can fill date gaps in MySQL? Here is my query:

SELECT DATE(posted_at) AS date,
    COUNT(*) AS total,
    SUM(attitude = 'positive') AS positive,
    SUM(attitude = 'neutral') AS neutral,
    SUM(attitude = 'negative') AS negative
    FROM `messages`
    WHERE (`messages`.brand_id = 1)
    AND (`messages`.`spam` = 0
    AND `messages`.`duplicate` = 0
    AND `messages`.`ignore` = 0)
    GROUP BY date ORDER BY date

It returns proper result set - but i want to fill gaps between dates start and end by zeros. How i can do this?

Answer 1

You'll need to create a helper table and fill it with all dates from start to end, then just LEFT JOIN with that table:

SELECT  d.dt AS date,
        COUNT(*) AS total,
        SUM(attitude = 'positive') AS positive,
        SUM(attitude = 'neutral') AS neutral,
        SUM(attitude = 'negative') AS negative
FROM    dates d
LEFT JOIN
        messages m
ON      m.posted_at >= d.dt
        AND m.posted_at < d.dt + INTERVAL 1 DAYS
        AND spam = 0
        AND duplicate = 0
        AND ignore = 0
GROUP BY
        d.dt
ORDER BY
        d.dt

Basically, what you need here is a dummy rowsource.

MySQL is the only major system which lacks a way to generate it.

PostgreSQL implements a special function generate_series to do that, while Oracle and SQL Server can use recursion (CONNECT BY and recursive CTEs, accordingly).