mysql多表選擇最近7天

Question

我有3個表，其中包含一些記錄有一個日期和一個數值（表不能被合併）。我想用表格中的信息組成條形圖。條形圖按日期分組，並應顯示最近七天。

早些時候，我有兩個表，並使用下面的查詢方案：

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) 

（僞代碼）

但我怎麼能做到這一點有超過2個表？ 是否有機會將過去7天的日期設置爲基準，以便每次獲得7條記錄？

指出問題：如果我沒有記錄在第一張表中的一天，我不會從那天的其他表中獲取記錄。

Answer 1

我假設3個表具有相似的模式？嘗試使用UNION ALL將表連接在一起。

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)