SQL

Question

代码（示例数据暂存）：

DECLARE @Emp TABLE
    (
        [EId] INT IDENTITY(1, 1)
      , [FN]  NVARCHAR(50)
      , [LN]  NVARCHAR(50)
    ) ;
DECLARE @EmpPhCont TABLE
    (
        [EId]       INT
      , [PhType]    VARCHAR(10)
      , [PhNum]     VARCHAR(16)
      , [PhExt]     VARCHAR(10)
      , [IsMain]    BIT
      , [CreatedOn] DATETIME
    ) ;

INSERT INTO @Emp
VALUES
    ( N'Emp1', N'Emp1' )
  , ( N'Emp2', N'Emp2' )
  , ( N'Emp3', N'Emp3' )
  , ( N'Emp4', N'Emp4' )
  , ( N'Emp5', N'Emp5' )
  , ( N'Emp6', N'Emp5' ) ;

INSERT INTO @EmpPhCont
VALUES
    ( 1, 'Home', '111111111', NULL, 0, '2020-01-01 00:00:01' )
  , ( 1, 'Mobile', '222222222', NULL, 1, '2020-01-01 00:00:02' )
  , ( 1, 'Work', '333333333', NULL, 0, '2020-01-01 00:00:03' )

  , ( 2, 'Work', '444444444', '567', 1, '2020-01-01 00:00:04' )
  , ( 2, 'Mobile', '555555555', NULL, 0, '2020-01-01 00:00:05' )
  , ( 2, 'Mobile', '454545454', NULL, 0, '2020-01-01 00:00:06' )

  , ( 3, 'Home', '777777777', NULL, 0, '2020-01-01 00:00:07' )
  , ( 3, 'Mobile', '888888888', NULL, 1, '2020-01-01 00:00:08' )
  , ( 3, 'Mobile', '12121212', NULL, 0, '2020-01-01 00:00:09' )

  , ( 4, 'Work', '101010101', '111', 1, '2020-01-01 00:00:10' )
  , ( 4, 'Work', '101010102', '232', 0, '2020-01-01 00:00:11' )

  , ( 5, 'Work', '545454545', '456', 0, '2020-01-01 00:00:10' )
  , ( 5, 'Work', '456456456', NULL, 1, '2020-01-01 00:00:11' )  ;

描述：

@Emp 是示例员工 table（唯一员工记录）。

EId = 员工编号
FN = 名字
LN = 姓氏

@EmpPhCont 是示例员工 Phone 联系人 table（来自@Emp table 的每个 Emp 在这里可以有零个、一个或多个 phone 数字 - 唯一通过 Emp/Type）。

PhType = Phone 类型（家庭、移动、工作等）
PhNum = Phone 数字
PhExt = Phone 扩展（主要用于 "Work" PhType）
IsMain = 是否是主要联系人号码。每个具有 phone num 的员工将恰好有 1 条记录标记为 IsMain。
CreatedOn = 创建记录的日期

目标：

为每个员工输出 1 条记录，包含以下列

EId | HomeNum | MobileNum | WorkNum | WorkNumExt | MainPhType

规则：

Return 来自@Emp 的所有记录的所有 EId，无论它们是否具有 @EmpPhCont 记录。

对于每个具有@EmpPhCont 记录可用的 emp，return 对应 PhType 的最新创建的 PhNum 和 PhExt，UNLESS 相同 Emp/PhType 被标记为 IsMain = 1（对于任何 emp，对于任何 PhType，如果 IsMain = 1，总是 return PhNum 和 PhExt 值）。

预期输出：

EId HomeNum     MobileNum   WorkNum     WorkNumExt  MainPhType
1   111111111   222222222   333333333   NULL        Mobile
2   NULL        454545454   444444444   567         Work
3   777777777   888888888   NULL        NULL        Mobile
4   NULL        NULL        101010102   111         Work
5   NULL        NULL        456456456   NULL        Work
6   NULL        NULL        NULL        NULL        NULL

我的失败尝试：

SELECT      [EM].[EId]
          , MAX ( IIF([PH].[PhType] = 'Home', [PH].[PhNum], NULL)) AS [HomePhNum]
          , MAX ( IIF([PH].[PhType] = 'Mobile', [PH].[PhNum], NULL)) AS [MobilePhNum]
          , MAX ( IIF([PH].[PhType] = 'Work', [PH].[PhNum], NULL)) AS [WorkPhNum]
FROM        @Emp AS [EM]
LEFT JOIN   @EmpPhCont AS [PH]
ON          [EM].[EId] = [PH].[EId]
GROUP BY    [EM].[EId] ;

Answer 1

我会使用 APPLY:

来实现

SELECT EId, HomeNum, MobileNum, WorkNum, WorkNumExt
     , COALESCE(HomeMain, MobileMain, WorkMain) AS MainPhType
  FROM Emp e
 OUTER APPLY (
          SELECT TOP 1 c.[PhNum] AS HomeNum
               , CASE WHEN c.[IsMain] = 1 THEN 'Home' END AS HomeMain
            FROM EmpPhCont c
           WHERE c.[EId] = e.[EId]
             AND c.[PhType] = 'Home'
           ORDER BY c.[IsMain] DESC, c.[CreatedOn] DESC
       ) home
 OUTER APPLY (
          SELECT TOP 1 c.[PhNum] AS MobileNum
               , CASE WHEN c.[IsMain] = 1 THEN 'Mobile' END AS MobileMain
            FROM EmpPhCont c
           WHERE c.[EId] = e.[EId]
             AND c.[PhType] = 'Mobile'
           ORDER BY c.[IsMain] DESC, c.[CreatedOn] DESC
       ) mobile
 OUTER APPLY (
          SELECT TOP 1 c.[PhNum] AS WorkNum
               , c.[PhExt] AS WorkNumExt
               , CASE WHEN c.[IsMain] = 1 THEN 'Work' END AS WorkMain
            FROM EmpPhCont c
           WHERE c.[EId] = e.[EId]
             AND c.[PhType] = 'Work'
           ORDER BY c.[IsMain] DESC, c.[CreatedOn] DESC
       ) work

有关演示，请参阅 SQL Fiddle。

输出

EId | HomeNum   | MobileNum | WorkNum   | WorkNumExt | MainPhType
1   | 111111111 | 222222222 | 333333333 | (null)     | Mobile
2   | (null)    | 454545454 | 444444444 | 567        | Work
3   | 777777777 | 888888888 | (null)    | (null)     | Mobile
4   | (null)    | (null)    | 101010101 | 111        | Work
5   | (null)    | (null)    | 456456456 | (null)     | Work
6   | (null)    | (null)    | (null)    | (null)     | (null)

注意： 如果 EmpPhCont table 在 [EId], [PhType] 上有索引，则此解决方案仅适用于大型数据集，否则会太慢了。

Answer 2

在 CTE 中使用 ROW_NUMBER() window 函数从 @EmpPhCont 中获取您想要返回的行并将此 CTE 连接到 @Emp:

with cte as (
  select *,
    row_number() over (partition by [EId], [PhType] order by [IsMain] desc, [CreatedOn] desc) rn
  from @EmpPhCont
)
select e.[EId],
  max(case when c.[PhType] = 'Home' then c.[PhNum] end) HomeNum,
  max(case when c.[PhType] = 'Mobile' then c.[PhNum] end) MobileNum,
  max(case when c.[PhType] = 'Work' then c.[PhNum] end) WorkNum,
  max(case when c.[PhType] = 'Work' then c.[PhExt] end) WorkNumExt,
  max(case when c.[IsMain] = 1 then c.[PhType] end) MainPhType 
from @Emp e left join cte c
on c.[EId] = e.[EId] and c.rn = 1
group by e.[EId]

参见demo。
结果：

> EId | HomeNum   | MobileNum | WorkNum   | WorkNumExt | MainPhType
> --: | :-------- | :-------- | :-------- | :--------- | :---------
>   1 | 111111111 | 222222222 | 333333333 | null       | Mobile    
>   2 | null      | 454545454 | 444444444 | 567        | Work      
>   3 | 777777777 | 888888888 | null      | null       | Mobile    
>   4 | null      | null      | 101010101 | 111        | Work      
>   5 | null      | null      | 456456456 | null       | Work      
>   6 | null      | null      | null      | null       | null

Answer 3

row_number()，外部应用和聚合：

select *
from @Emp as e
outer apply
(
    select 
          MAX ( case when d.[PhType] = 'Home' then d.[PhNum] end) AS [HomePhNum]
        , MAX ( case when d.[PhType] = 'Mobile' then d.[PhNum] end) AS [MobilePhNum]
        , MAX ( case when d.[PhType] = 'Work' then d.[PhNum] end) AS [WorkPhNum]
        , MAX ( case when d.[PhType] = 'Work' then d.[PhExt] end) AS [WorkNumExt]
        , MAX ( case when IsMain = 1 then d.[PhType] end) AS MainPhType --work is max if both mob&work as set as main..
    from
    (
    select *, row_number() over(partition by PhType order by IsMain DESC, CreatedOn DESC) as rownum
    from @EmpPhCont as p
    where p.EId = e.EId
    ) as d
    where d.rownum = 1  
) as ph;

SQL - 父子（1 到 zero/many）Grouping/Aggregation

TSQL - Parent Child (1 to zero/many) Grouping/Aggregation

tsql

sql-server

sql-server-2016