Unpivot T-sql Query | 易学教程

问题

following is the result of my query

Year_Month.........cat1_per......cat2_per........cat3_per......cat4_per
2004_06...............0.892..........0.778............0.467..........0.871
2005_10...............0.790..........0.629............0.581..........0.978

but i want output of my query to be

Category...........2004_06..............2005_10
cat1_per.............0.892..................0.790
cat2_per.............0.778..................0.629
cat3_per.............0.467..................0.581
cat4_per.............0.871..................0.978

what is the best way to do it? any help is appreciated. I tried Unpivot but was not able to get desired result.

回答1:

You did not specify the RDBMS but since you tagged it tsql I am guessing sql-server. This is actually both an UNPIVOT and then a PIVOT. If you know the values that you need to transform, then you can hard-code them via a static version:

select *
from
(
  select year_month, value, category
  from table1
  unpivot
  (
    value
    for category in (cat1_per, cat2_per, cat3_per, cat4_per)
  ) un
) x
pivot
(
  max(value)
  for year_month in ([2004_06], [2005_10])
)p

See SQL Fiddle With Demo

If you then have a unknown number of values to transform, then you can use a dynamic sql pivot:

DECLARE @colsUnpivot AS NVARCHAR(MAX),
    @query  AS NVARCHAR(MAX),
    @colsPivot as  NVARCHAR(MAX)

select @colsUnpivot = stuff((select ','+quotename(C.name)
         from sys.columns as C
         where C.object_id = object_id('Table1') and
               C.name like 'cat%per'
         for xml path('')), 1, 1, '')

select @colsPivot = STUFF((SELECT  ',' 
                      + quotename(t.year_month)
                    from Table1 t
            FOR XML PATH(''), TYPE
            ).value('.', 'NVARCHAR(MAX)') 
        ,1,1,'')


set @query 
  = 'select *
      from
      (
        select year_month, value, category
        from table1
        unpivot
        (
          value
          for category in ('+ @colsunpivot +')
        ) un
      ) x
      pivot
      (
        max(value)
        for year_month in ('+ @colspivot +')
      ) p'

exec(@query)

See SQL Fiddle with demo

Both will produce the same results:

| CATEGORY | 2004_06 | 2005_10 |
--------------------------------
| cat1_per |   0.892 |    0.79 |
| cat2_per |   0.778 |   0.629 |
| cat3_per |   0.467 |   0.581 |
| cat4_per |   0.871 |   0.978 |

If for some reason, you did not have the UNPIVOT and PIVOT functions then you can replicate this using a combination of UNION ALL to unpivot and then a CASE statement and an aggregate function to pivot:

select category,
  max(case when year_month = '2004_06' then value end) [2004_06],
  max(case when year_month = '2005_10' then value end) [2005_10]
from
(
  select year_month, cat1_per value, 'cat1_per' category
  from table1
  union all
  select year_month, cat2_per value, 'cat2_per' category
  from table1
  union all
  select year_month, cat3_per value, 'cat3_per' category
  from table1
  union all
  select year_month, cat4_per value, 'cat4_per' category
  from table1
) un
group by category

See SQL Fiddle with Demo

来源：https://stackoverflow.com/questions/12935311/unpivot-t-sql-query

标签

tsql

pivot

unpivot