试图将行压平成列

Question

我在表中有一组具有id的行.我试图在多列的行中展平它.我几乎可以肯定我用cte和也许分区完成了这个.

我用cte来删除重复的数据,我以为我做了类似于我想要完成的事情.我能够提出可行的解决方案(如下所列),但仍然觉得应该有更优雅的解决方案.

CREATE TABLE #MyTable ( RowID int , field VARCHAR(10), value  VARCHAR(10))  

INSERT INTO #MyTable ( RowID, field, value ) VALUES  ( 1, 'first', 'neil' )

INSERT INTO #MyTable ( RowID, field, value ) VALUES  ( 2, 'first', 'bob'  )

INSERT INTO #MyTable ( RowID, field, value ) VALUES  ( 3, 'first', 'tom'  )

INSERT INTO #MyTable ( RowID, field, value ) VALUES  ( 1, 'last', 'young' )

INSERT INTO #MyTable ( RowID, field, value ) VALUES  ( 2, 'last', 'dylan' )

INSERT INTO #MyTable ( RowID, field, value ) VALUES  ( 3, 'last', 'petty' )

SELECT * FROM #mytable

- 使用cte/partition完成此操作:

SELECT rowid, 
   [first] = (Select value FROM #mytable where field = 'first' and rowid = t.rowid), 
   [last] = (Select value FROM #mytable where field = 'last' and rowid = t.rowid)
FROM #mytable t
GROUP BY rowid

Answer 1

这种数据转换称为a PIVOT.在SQL Server 2005+中,有一个函数将执行此过程.:

select *
from
(
  SELECT * 
  FROM mytable
) src
pivot
(
  max(value)
  for field in (first, last)
) piv

请参阅SQL Fiddle with Demo.

或者您可以将聚合函数与CASE表达式一起使用:

select rowid,
  max(case when field = 'first' then value end) first,
  max(case when field = 'last' then value end) last
from MyTable
group by rowid

请参阅SQL Fiddle with Demo.

您还可以在表上使用多个连接:

select t1.rowid,
  t1.value first,
  t2.value last
from mytable t1
left join mytable t2
  on t1.rowid = t2.rowid
  and t2.field = 'last'
where t1.field = 'first'

请参阅SQL Fiddle with Demo

所有版本的结果都是相同的:

| ROWID | FIRST |  LAST |
-------------------------
|     1 |  neil | young |
|     2 |   bob | dylan |
|     3 |   tom | petty |