mysql - mysql 多表选择过去 7 天

Question

我有 3 个表，其中包含一些具有日期和数值的记录（这些表无法合并）。我想使用表格中的信息制作条形图。条形图按天分组，应显示最近 7 天。

早些时候我有两个表并使用以下查询方案：

SELECT
    t.credits1,
    t.credits2,
    t.date
FROM
    (
        (
            SELECT
                t1.credits1,
                t2.credits2,
                t1.date
            FROM
                (
                    SELECT
                        SUM(credits) AS credits1,
                        date
                    FROM
                        table1
                    WHERE
                        table1.date >= DATE_SUB(CURDATE(), INTERVAL 7 DAY)
                    GROUP BY
                        DATE(table1.date)
                ) t1

                LEFT JOIN
                (
                    SELECT
                        SUM(credits) AS credits2,
                        date
                    FROM
                        table2
                    WHERE
                        table2.date >= DATE_SUB(CURDATE(), INTERVAL 7 DAY)
                    GROUP BY
                        DATE(table2.date)
                ) t2
                ON t1.date = t2.date
        )
        UNION
        (
            SELECT
                t1.credits1,
                t2.credits2,
                t1.date
            FROM
                (
                    SELECT
                        SUM(credits) AS credits1,
                        date
                    FROM
                        table1
                    WHERE
                        table1.date >= DATE_SUB(CURDATE(), INTERVAL 7 DAY)
                    GROUP BY
                        DATE(table1.date)
                ) t1

                RIGHT JOIN
                (
                    SELECT
                        SUM(credits) AS credits2,
                        date
                    FROM
                        table2
                    WHERE
                        table2.date >= DATE_SUB(CURDATE(), INTERVAL 7 DAY)
                    GROUP BY
                        DATE(table2.date)
                ) t2
                ON t1.date = t2.date
        )
    ) t GROUP BY
DATE(date)

（伪代码）

但是我怎么能用超过 2 张桌子做到这一点？有没有机会以过去 7 天的日期为基准，这样我每次都能得到 7 条记录？

指出问题：如果我在第一个表中没有记录一天，我将不会从其他表中获取当天的记录。

Answer 1

我假设这 3 个表具有相似的模式？尝试使用 UNION ALL 将表连接在一起。

SELECT ABB1.date, SUM(ABB1.credit) AS daily_total
FROM
    (SELECT date, credits
    FROM table1

    UNION ALL 

    SELECT date, credits
    FROM table1

    UNION ALL 

    SELECT date, credits
    FROM table2) AS ABB1
WHERE DATE >= DATE_SUB(CURDATE(), INTERVAL 7 DAY)