Question

我有两个试图要加入的表，但没有得到预期的结果。

一个房间在不同的日期有多个孩子，但是，只有在孩子开始营业并且当天分配了小时后，才将这些孩子计入一个房间。我想要实现的输出就是这个。

Room  | MaxNum | Mon(Week1) | Tue(Week1) | Mon(Week2) | Tue(Week2)
Blue  | 5      | 4          | 4          | 3          | 2
Green | 10     | 10         | 10         | 9          | 9  
Red   | 15     | 15         | 15         | 15         | 15

这是架构和一些数据...

create table Rooms(
  id       INT,
  RoomName VARCHAR(10),
  MaxNum   INT
);

create table Children (
  id          INT,
  RoomID      INT,
  MonHrs      INT,
  TueHrs      INT,
  StartDate   DATE
);

INSERT INTO Rooms VALUES (1, 'Blue', 5);
INSERT INTO Rooms VALUES (2, 'Green', 10);
INSERT INTO Rooms VALUES (3, 'Red', 15);

INSERT INTO Children VALUES (1, 1, 5, 0, '2018-12-02');
INSERT INTO Children VALUES (2, 1, 0, 5, '2018-12-02');
INSERT INTO Children VALUES (3, 1, 5, 5, '2018-12-09');
INSERT INTO Children VALUES (4, 1, 0, 5, '2018-12-09');
INSERT INTO Children VALUES (5, 2, 5, 0, '2018-12-09');
INSERT INTO Children VALUES (6, 2, 0, 5, '2018-12-09');

我遇到麻烦的SQL是这个。这可能不是正确的方法。

SELECT R.RoomName, R.MaxNum,
       R.MaxNum - SUM(CASE WHEN C1.MonHrs > 0 THEN 1 ELSE 0 END) AS Mon1,
       R.MaxNum - SUM(CASE WHEN C1.TueHrs > 0 THEN 1 ELSE 0 END) AS Tue1,
       R.MaxNum - SUM(CASE WHEN C2.MonHrs > 0 THEN 1 ELSE 0 END) AS Mon2,
       R.MaxNum - SUM(CASE WHEN C2.TueHrs > 0 THEN 1 ELSE 0 END) AS Tue2
  FROM Rooms R
        LEFT JOIN Children C1 
          ON R.id = C1.RoomID
         AND C1.StartDate <= '2018-12-02'     
        LEFT JOIN Children C2
          ON R.id = C2.RoomID
         AND C2.StartDate <= '2018-12-09'
 GROUP BY R.RoomName;

LEFT JOIN中的Rows发生了双重故障，导致计数失效，我不知道该如何防止。如果将SELECT替换为*

，则可以看到效果

任何建议都会有很大帮助。

Answer 1

这种问题通常是由于在查询中过于宽泛的位置进行了汇总而导致的，然后导致记录的重复计数。尝试在单独的子查询中汇总Children表：

SELECT
    R.RoomName,
    R.MaxNum,
    R.MaxNum - C.Mon1 AS Mon1,
    R.MaxNum - C.Tue1 AS Tue1,
    R.MaxNum - C.Mon2 AS Mon2,
    R.MaxNum - C.Tue2 AS Tue2
FROM Rooms R
LEFT JOIN
(
    SELECT
        RoomID,
        COUNT(CASE WHEN MonHrs > 0 AND StartDate <= '2018-12-02'
                   THEN 1 END) AS Mon1,
        COUNT(CASE WHEN TueHrs > 0 AND StartDate <= '2018-12-02'
                   THEN 1 END) AS Tue1,
        COUNT(CASE WHEN MonHrs > 0 AND StartDate <= '2018-12-09'
                   THEN 1 END) AS Mon2,
        COUNT(CASE WHEN TueHrs > 0 AND StartDate <= '2018-12-09'
                   THEN 1 END) AS Tue2
    FROM Children
    GROUP BY RoomID
) C
    ON R.id = C.RoomID;

请注意，我们可以通过在开始日期使用条件汇总来避免原始查询中的两次左联接。

最新编辑：您甚至可能根本不需要子查询。 @Salman的答案。但是我们的任何一个答案都可以解决重复计算的问题。

Answer 2

您需要使用 one 左联接并将日期过滤器从“联接”条件移至汇总：

SELECT R.id, R.RoomName, R.MaxNum
    , R.MaxNum - COUNT(CASE WHEN C.StartDate <= '2018-12-02' AND C.MonHrs > 0 THEN 1 END) AS Mon1
    , R.MaxNum - COUNT(CASE WHEN C.StartDate <= '2018-12-02' AND C.TueHrs > 0 THEN 1 END) AS Tue1
    , R.MaxNum - COUNT(CASE WHEN C.StartDate <= '2018-12-09' AND C.MonHrs > 0 THEN 1 END) AS Mon2
    , R.MaxNum - COUNT(CASE WHEN C.StartDate <= '2018-12-09' AND C.TueHrs > 0 THEN 1 END) AS Tue2
FROM Rooms R
LEFT JOIN Children C ON R.id = C.RoomID
GROUP BY R.id, R.RoomName, R.MaxNum

在同一表上左联接加倍行

2 个答案: