SQL Server convert columns to rows

问题:

I have a sql table with current value and previous value.

Id  Value1  PValue1 Value2  PValue2
1   A       A       V       V1
2   B       B1      W       W1
3   C       C1      X       X

I want to compare them and display in a the following table if the value has changes.

Id  Column  Value   Pvalue
1   Value2  V       V1
2   Value1  B       B1
2   Value2  W       W1
3   Value1  C       C1

Is it possible in SQL 2008 without looping each column?

回答1:

You can use a CROSS APPLY to unpivot the data:

SELECT t.id,
  x.Col,
  x.Value,
  x.PValue
FROM YourTable t
CROSS APPLY 
(
    VALUES
        ('Value1', t.Value1, t.PValue1),
        ('Value2', t.Value2, t.PValue2)
) x (Col, Value, PValue)
where x.Value <> x.PValue;

See SQL Fiddle with Demo.

Just because I love using the pivot function, here is a version that uses both the unpivot and the pivot functions to get the result:

select id, 
  colname,
  value,
  pvalue
from
(
  select id, 
    replace(col, 'P', '') colName,
    substring(col, 1, PatIndex('%[0-9]%', col) -1) new_col,  
    val
  from yourtable
  unpivot
  (
    val
    for col in (Value1, PValue1, Value2, PValue2)
  ) unpiv
) src
pivot
(
  max(val)
  for new_col in (Value, PValue)
) piv
where value <> pvalue
order by id

See SQL Fiddle with Demo

回答2:

Here is an easy way:

SELECT  Id, 
        'Value1' [Column],
        Value1 Value,
        PValue1 PValue
FROM YourTable
WHERE ISNULL(Value1,'') != ISNULL(PValue1,'')
UNION ALL
SELECT  Id, 
        'Value2' [Column],
        Value2 Value,
        PValue2 PValue
FROM YourTable
WHERE ISNULL(Value2,'') != ISNULL(PValue2,'')

回答3:

How about using a union:

SELECT * FROM
    (SELECT Id, 'Value1' [Column], Value1 [Value], PValue1 [PValue]
    FROM table_name
    UNION ALL
    SELECT Id, 'Value2' [Column], Value2 [Value], PValue2 [PValue]
    FROM table_name)tmp
WHERE Value != PValue
ORDER BY Id

回答4:

Finally, and for completeness, there is an UNPIVOT command. However, since you have two columns you want to unpivot, it'd probably be simpler to use one of the other solutions.