Question

我目前有一个非常简单的查询，可以简单地选择并生成以下内容

| Date       | Name             | ID      |
|------------|------------------|---------|
| 2018-11-07 | McDonald's       | 1046226 |
| 2018-01-22 | NULL             | 1046226 |
| 2019-01-07 | Dell             | 1069285 |
| 2019-01-09 | Dell Corporation | 1069285 |

我想做的是使用MIN为每个ID选择最早的日期行

但是我的问题是，如果最早的行名称为NULL，我想从另一行合并其名称

| Date       | Name             | ID      |
|------------|------------------|---------|
| 2018-01-22 | McDonald's       | 1046226 |
| 2019-01-07 | Dell             | 1069285 |

我不知道是否有任何语法可以在这里帮助我，有人可以帮助吗？

Answer 1

使用coalesce：

select 
  min(t.date) Date,
  coalesce(
    (
      select name from tablename where id = t.id and date = (
        select min(date) from tablename where id = t.id
      )
    ),
    max(name)
  ) name,
  t.id ID
from tablename t
group by t.id

Answer 2

通常，row_number()用于此目的：

select t.*
from (select t.*, row_number() over (partition by id order by date) as seqnum
      from <your query here> t
     ) t
where seqnum = 1;

一种稍微慢一点的简单方法是：

select top (1) with ties . . .
from . . .
. . .
order by row_number() over (partition by id order by date)

Answer 3

使用CTE在Azure SQL数据仓库上测试的两种方法

import { FormsModule, ReactiveFormsModule } from "@angular/forms"; //this to use ngModule

或者，如果您要将剩余数据CTAS到新表中，则可以在Azure SQL数据仓库中将CTE和CTAS结合起来，例如

imports: [
    BrowserModule,
    AppRoutingModule,
    HttpModule,
    FormsModule,
    RouterModule,
    ReactiveFormsModule,
    BrowserAnimationsModule,
    MaterialModule],

请注意;WITH cte AS ( SELECT *, ROW_NUMBER() OVER( PARTITION BY ID ORDER BY [Date] ) rn FROM #tmp ) SELECT [Date], name, ID FROM cte WHERE rn = 1和CREATE TABLE dbo.yourNewTable WITH ( CLUSTERED COLUMNSTORE INDEX, DISTRIBUTION = HASH( ID ) -- Optionally add partition scheme here if required ) AS WITH cte AS ( SELECT [Date], MIN(Name) OVER( PARTITION BY ID ) name, ID, ROW_NUMBER() OVER( PARTITION BY ID ORDER BY [Date] ) rn FROM dbo.yourTable ) SELECT [Date], name, ID FROM cte WHERE rn = 1 OPTION ( LABEL = 'CTAS : Dedupe' );在行为上的差异。

TSQL合并行值

3 个答案: