SQL Server 2012：旋转（？）固定行数作为列

Question

我有一辆 table 叫车：

CREATE TABLE [dbo].[Car](
    [ID] [int] IDENTITY(1,1) NOT NULL,
    [Brand] [nchar](10) NOT NULL
)

还有一个叫 Passenger：

CREATE TABLE [dbo].[Passenger](
    [ID] [int] IDENTITY(1,1) NOT NULL,
    [CarID] [int] NOT NULL,
    [Name] [nchar](10) NOT NULL
)

包含以下数据：

+----+------------+
| ID |   Brand    |
+----+------------+
|  1 | Ford       |
|  2 | Audi       |
+----+------------+

+----+-------+------------+
| ID | CarID |    Name    |
+----+-------+------------+
|  1 |     1 | Joe        |
|  2 |     1 | Jack       |
|  3 |     1 | Jim        |
|  4 |     2 | Bob        |
|  5 |     2 | Frank      |
+----+-------+------------+

另外，我限制一辆车的乘客人数=5。（业务逻辑）

我想做的是在视图 table 中显示此数据，如下例所示：

+----+------------+------------+------------+------------+------------+------------+
| ID |   Brand    | Passenger1 | Passenger2 | Passenger3 | Passenger4 | Passenger5 |
+----+------------+------------+------------+------------+------------+------------+
|  1 | Ford       | Joe        | Jack       | Jim        | NULL       | NULL       |
|  2 | Audi       | Bob        | Frank      | NULL       | NULL       | NULL       |
+----+------------+------------+------------+------------+------------+------------+

因此，如果乘客少于 5 人，则其余列为 NULL，我们不需要处理超过 5 名乘客。

并不是真的需要乘客的排序，但 NULLs 必须在最后（例如 Frank, Bob, NULL, NULL, NULL is OK for Car ID 2, but Frank, NULL, NULL, Bob, NULL 不是。）如果也可以对乘客进行排序，那么我更愿意按 ID 排序。

如何使用 SQL Server 2012 进行数据转换？

Answer 1

使用 Pivot 运算符对数据进行透视

使用 Row_number window 函数生成乘客编号，这样没有所有 5 名乘客的车厢最后会有 NULL 个值

;WITH cte
     AS (SELECT c.id,
                c.Brand,
                'Passenger'+ Cast(Row_number() OVER(partition BY c.id ORDER BY p.id) AS VARCHAR(50)) p_name,
                NAME
         FROM   [Car] c
                JOIN [Passenger] p
                  ON c.ID = p.CarID)
SELECT *
FROM   cte
       PIVOT (Max(NAME)
             FOR p_name IN(Passenger1,
                           Passenger2,
                           Passenger3,
                           Passenger4,
                           Passenger5 ))pv
ORDER  BY id

Conditional Aggregate方法

;WITH cte
     AS (SELECT c.id,
                c.Brand,
                'Passenger'+ Cast(Row_number() OVER(partition BY c.id ORDER BY p.id) AS VARCHAR(50)) p_name,
                NAME
         FROM   [Car] c
                JOIN Passenger p
                  ON c.ID = p.CarID)
SELECT id,
       Brand,
       [Passenger1]=Max(CASE WHEN p_name = 'Passenger1' THEN NAME END),
       [Passenger2]=Max(CASE WHEN p_name = 'Passenger2' THEN NAME END),
       [Passenger3]=Max(CASE WHEN p_name = 'Passenger3' THEN NAME END),
       [Passenger4]=Max(CASE WHEN p_name = 'Passenger4' THEN NAME END),
       [Passenger5]=Max(CASE WHEN p_name = 'Passenger5' THEN NAME END)
FROM   cte
GROUP  BY id,
          Brand
ORDER  BY id

结果：

╔════╦════════════╦════════════╦════════════╦════════════╦════════════╦════════════╗
║ id ║   Brand    ║ Passenger1 ║ Passenger2 ║ Passenger3 ║ Passenger4 ║ Passenger5 ║
╠════╬════════════╬════════════╬════════════╬════════════╬════════════╬════════════╣
║  1 ║ Ford       ║ Joe        ║ Jack       ║ Jim        ║ NULL       ║ NULL       ║
║  2 ║ Audi       ║ Bob        ║ Frank      ║ NULL       ║ NULL       ║ NULL       ║
╚════╩════════════╩════════════╩════════════╩════════════╩════════════╩════════════╝

Answer 2

未测试：

我们使用 row_num() 按卡 ID 分区以获得 5 个位置的固定座位号添加 P 因为我不确定 SQL 服务器是否可以有一个列星号编号，然后根据这 5 个派生值对数据进行透视。

Select brand, P1, P2, P3, P4, P5
FROM 
  (
  SELECT brand, name, 'P' & row_Number() Over (partition by CarID order by P.name) as PNum
  FROM car C
  INNER JOIN passenger P
    on C.CardID = P.CardID
  ) src
  PIVOT 
  (
    max(src.name)
    FOr pnum in ([P1],[P2],[P3],[P4],[P5])
  ) as PT

SQL Server 2012：旋转（？）固定行数作为列

SQL Server 2012: Pivoting(?) fixed number of rows as columns

sql-server

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