sql - 如何填补 MySQL 中的日期空白？

Question

如何填补 MySQL 中的日期空白？这是我的查询:

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

它返回正确的结果集 - 但我想用零填充日期开始和结束之间的空白。我怎样才能做到这一点？

Answer 1

您需要创建一个辅助表，并用从 start 到 end 的所有日期填充它，然后只需 LEFT JOIN 即可表:

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

基本上，您在这里需要的是一个虚拟行源。

MySQL 是唯一缺少生成它的方法的主要系统。

PostgreSQL 实现了一个特殊函数 generate_series 来执行此操作，而 Oracle 和 SQL Server 可以使用递归(相应地，CONNECT BY 和递归CTE)。