Efficiently convert rows to columns in sql server

Question

I'm looking for an efficient way to convert rows to columns in SQL server, I heard that PIVOT is not very fast, and I need to deal with lot of records.

This is my example:

   -------------------------------    | Id | Value  | ColumnName    |    -------------------------------    | 1  | John   | FirstName     |    | 2  | 2.4    | Amount        |    | 3  | ZH1E4A | PostalCode    |    | 4  | Fork   | LastName      |    | 5  | 857685 | AccountNumber |    ------------------------------- 

This is my result:

--------------------------------------------------------------------- | FirstName  |Amount|   PostalCode   |   LastName  |  AccountNumber | --------------------------------------------------------------------- | John       | 2.4  |   ZH1E4A       |   Fork      |  857685        | --------------------------------------------------------------------- 

How can I build the result?

Answer 1

There are several ways that you can transform data from multiple rows into columns.

Using PIVOT

In SQL Server you can use the PIVOT function to transform the data from rows to columns:

select Firstname, Amount, PostalCode, LastName, AccountNumber from (   select value, columnname   from yourtable ) d pivot (   max(value)   for columnname in (Firstname, Amount, PostalCode, LastName, AccountNumber) ) piv; 

See Demo.

Pivot with unknown number of columnnames

If you have an unknown number of columnnames that you want to transpose, then you can use dynamic SQL:

DECLARE @cols AS NVARCHAR(MAX),     @query  AS NVARCHAR(MAX)  select @cols = STUFF((SELECT ',' + QUOTENAME(ColumnName)                      from yourtable                     group by ColumnName, id                     order by id             FOR XML PATH(''), TYPE             ).value('.', 'NVARCHAR(MAX)')          ,1,1,'')  set @query = N'SELECT ' + @cols + N' from               (                 select value, ColumnName                 from yourtable             ) x             pivot              (                 max(value)                 for ColumnName in (' + @cols + N')             ) p '  exec sp_executesql @query; 

See Demo.

Using an aggregate function

If you do not want to use the PIVOT function, then you can use an aggregate function with a CASE expression:

select   max(case when columnname = 'FirstName' then value end) Firstname,   max(case when columnname = 'Amount' then value end) Amount,   max(case when columnname = 'PostalCode' then value end) PostalCode,   max(case when columnname = 'LastName' then value end) LastName,   max(case when columnname = 'AccountNumber' then value end) AccountNumber from yourtable 

See Demo.

Using multiple joins

This could also be completed using multiple joins, but you will need some column to associate each of the rows which you do not have in your sample data. But the basic syntax would be:

select fn.value as FirstName,   a.value as Amount,   pc.value as PostalCode,   ln.value as LastName,   an.value as AccountNumber from yourtable fn left join yourtable a   on fn.somecol = a.somecol   and a.columnname = 'Amount' left join yourtable pc   on fn.somecol = pc.somecol   and pc.columnname = 'PostalCode' left join yourtable ln   on fn.somecol = ln.somecol   and ln.columnname = 'LastName' left join yourtable an   on fn.somecol = an.somecol   and an.columnname = 'AccountNumber' where fn.columnname = 'Firstname' 

Answer 2

This is rather a method than just a single script but gives you much more flexibility.

First of all There are 3 objects:

1. User defined TABLE type [ColumnActionList] -> holds data as parameter
2. SP [proc_PivotPrepare] -> prepares our data
3. SP [proc_PivotExecute] -> execute the script

CREATE TYPE [dbo].[ColumnActionList] AS TABLE ( [ID] [smallint] NOT NULL, [ColumnName] nvarchar NOT NULL, [Action] nchar NOT NULL ); GO

    CREATE PROCEDURE [dbo].[proc_PivotPrepare]      (     @DB_Name        nvarchar(128),     @TableName      nvarchar(128)     )     AS             SELECT @DB_Name = ISNULL(@DB_Name,db_name())     DECLARE @SQL_Code nvarchar(max)      DECLARE @MyTab TABLE (ID smallint identity(1,1), [Column_Name] nvarchar(128), [Type] nchar(1), [Set Action SQL] nvarchar(max));      SELECT @SQL_Code        =   'SELECT [<| SQL_Code |>] = '' '' '                                         + 'UNION ALL '                                         + 'SELECT ''----------------------------------------------------------------------------------------------------'' '                                         + 'UNION ALL '                                         + 'SELECT ''-----| Declare user defined type [ID] / [ColumnName] / [PivotAction] '' '                                         + 'UNION ALL '                                         + 'SELECT ''----------------------------------------------------------------------------------------------------'' '                                         + 'UNION ALL '                                         + 'SELECT ''DECLARE @ColumnListWithActions ColumnActionList;'''                                         + 'UNION ALL '                                         + 'SELECT ''----------------------------------------------------------------------------------------------------'' '                                         + 'UNION ALL '                                         + 'SELECT ''-----| Set [PivotAction] (''''S'''' as default) to select dimentions and values '' '                                         + 'UNION ALL '                                         + 'SELECT ''-----|'''                                         + 'UNION ALL '                                         + 'SELECT ''-----| ''''S'''' = Stable column || ''''D'''' = Dimention column || ''''V'''' = Value column '' '                                         + 'UNION ALL '                                         + 'SELECT ''----------------------------------------------------------------------------------------------------'' '                                         + 'UNION ALL '                                         + 'SELECT ''INSERT INTO  @ColumnListWithActions VALUES ('' + CAST( ROW_NUMBER() OVER (ORDER BY [NAME]) as nvarchar(10)) + '', '' + '''''''' + [NAME] + ''''''''+ '', ''''S'''');'''                                         + 'FROM [' + @DB_Name + '].sys.columns  '                                         + 'WHERE object_id = object_id(''[' + @DB_Name + ']..[' + @TableName + ']'') '                                         + 'UNION ALL '                                         + 'SELECT ''----------------------------------------------------------------------------------------------------'' '                                         + 'UNION ALL '                                         + 'SELECT ''-----| Execute sp_PivotExecute with parameters: columns and dimentions and main table name'' '                                         + 'UNION ALL '                                         + 'SELECT ''----------------------------------------------------------------------------------------------------'' '                                         + 'UNION ALL '                                         + 'SELECT ''EXEC [dbo].[sp_PivotExecute] @ColumnListWithActions, ' + '''''' + @TableName + '''''' + ';'''                                         + 'UNION ALL '                                         + 'SELECT ''----------------------------------------------------------------------------------------------------'' '                             EXECUTE SP_EXECUTESQL @SQL_Code;  GO  CREATE PROCEDURE [dbo].[sp_PivotExecute] ( @ColumnListWithActions  ColumnActionList ReadOnly ,@TableName                     nvarchar(128) ) AS   --####################################################################################################################### --###| Step 1 - Select our user-defined-table-variable into temp table --#######################################################################################################################  IF OBJECT_ID('tempdb.dbo.#ColumnListWithActions', 'U') IS NOT NULL DROP TABLE #ColumnListWithActions;  SELECT * INTO #ColumnListWithActions FROM @ColumnListWithActions;  --####################################################################################################################### --###| Step 2 - Preparing lists of column groups as strings: --#######################################################################################################################  DECLARE @ColumnName                     nvarchar(128) DECLARE @Destiny                        nchar(1)  DECLARE @ListOfColumns_Stable           nvarchar(max) DECLARE @ListOfColumns_Dimension    nvarchar(max) DECLARE @ListOfColumns_Variable     nvarchar(max) --############################ --###| Cursor for List of Stable Columns --############################  DECLARE ColumnListStringCreator_S CURSOR FOR SELECT      [ColumnName] FROM        #ColumnListWithActions WHERE       [Action] = 'S' OPEN ColumnListStringCreator_S; FETCH NEXT FROM ColumnListStringCreator_S INTO @ColumnName   WHILE @@FETCH_STATUS = 0     BEGIN         SELECT @ListOfColumns_Stable = ISNULL(@ListOfColumns_Stable, '') + ' [' + @ColumnName + '] ,';         FETCH NEXT FROM ColumnListStringCreator_S INTO @ColumnName    END  CLOSE ColumnListStringCreator_S; DEALLOCATE ColumnListStringCreator_S;  --############################ --###| Cursor for List of Dimension Columns --############################  DECLARE ColumnListStringCreator_D CURSOR FOR SELECT      [ColumnName] FROM        #ColumnListWithActions WHERE       [Action] = 'D' OPEN ColumnListStringCreator_D; FETCH NEXT FROM ColumnListStringCreator_D INTO @ColumnName   WHILE @@FETCH_STATUS = 0     BEGIN         SELECT @ListOfColumns_Dimension = ISNULL(@ListOfColumns_Dimension, '') + ' [' + @ColumnName + '] ,';         FETCH NEXT FROM ColumnListStringCreator_D INTO @ColumnName    END  CLOSE ColumnListStringCreator_D; DEALLOCATE ColumnListStringCreator_D;  --############################ --###| Cursor for List of Variable Columns --############################  DECLARE ColumnListStringCreator_V CURSOR FOR SELECT      [ColumnName] FROM        #ColumnListWithActions WHERE       [Action] = 'V' OPEN ColumnListStringCreator_V; FETCH NEXT FROM ColumnListStringCreator_V INTO @ColumnName   WHILE @@FETCH_STATUS = 0     BEGIN         SELECT @ListOfColumns_Variable = ISNULL(@ListOfColumns_Variable, '') + ' [' + @ColumnName + '] ,';         FETCH NEXT FROM ColumnListStringCreator_V INTO @ColumnName    END  CLOSE ColumnListStringCreator_V; DEALLOCATE ColumnListStringCreator_V;  SELECT @ListOfColumns_Variable      = LEFT(@ListOfColumns_Variable, LEN(@ListOfColumns_Variable) - 1); SELECT @ListOfColumns_Dimension = LEFT(@ListOfColumns_Dimension, LEN(@ListOfColumns_Dimension) - 1); SELECT @ListOfColumns_Stable            = LEFT(@ListOfColumns_Stable, LEN(@ListOfColumns_Stable) - 1);  --####################################################################################################################### --###| Step 3 - Preparing table with all possible connections between Dimension columns excluding NULLs --####################################################################################################################### DECLARE @DIM_TAB TABLE ([DIM_ID] smallint, [ColumnName] nvarchar(128)) INSERT INTO @DIM_TAB  SELECT [DIM_ID] = ROW_NUMBER() OVER(ORDER BY [ColumnName]), [ColumnName] FROM #ColumnListWithActions WHERE [Action] = 'D';  DECLARE @DIM_ID smallint; SELECT      @DIM_ID = 1;   DECLARE @SQL_Dimentions nvarchar(max);  IF OBJECT_ID('tempdb.dbo.##ALL_Dimentions', 'U') IS NOT NULL DROP TABLE ##ALL_Dimentions;   SELECT @SQL_Dimentions      = 'SELECT [xxx_ID_xxx] = ROW_NUMBER() OVER (ORDER BY ' + @ListOfColumns_Dimension + '), ' + @ListOfColumns_Dimension                                             + ' INTO ##ALL_Dimentions '                                             + ' FROM (SELECT DISTINCT' + @ListOfColumns_Dimension + ' FROM  ' + @TableName                                             + ' WHERE ' + (SELECT [ColumnName] FROM @DIM_TAB WHERE [DIM_ID] = @DIM_ID) + ' IS NOT NULL ';                                             SELECT @DIM_ID = @DIM_ID + 1;             WHILE @DIM_ID <= (SELECT MAX([DIM_ID]) FROM @DIM_TAB)             BEGIN             SELECT @SQL_Dimentions = @SQL_Dimentions + 'AND ' + (SELECT [ColumnName] FROM @DIM_TAB WHERE [DIM_ID] = @DIM_ID) +  ' IS NOT NULL ';             SELECT @DIM_ID = @DIM_ID + 1;             END  SELECT @SQL_Dimentions   = @SQL_Dimentions + ' )x';  EXECUTE SP_EXECUTESQL  @SQL_Dimentions;  --####################################################################################################################### --###| Step 4 - Preparing table with all possible connections between Stable columns excluding NULLs --####################################################################################################################### DECLARE @StabPos_TAB TABLE ([StabPos_ID] smallint, [ColumnName] nvarchar(128)) INSERT INTO @StabPos_TAB  SELECT [StabPos_ID] = ROW_NUMBER() OVER(ORDER BY [ColumnName]), [ColumnName] FROM #ColumnListWithActions WHERE [Action] = 'S';  DECLARE @StabPos_ID smallint; SELECT      @StabPos_ID = 1;   DECLARE @SQL_MainStableColumnTable nvarchar(max);  IF OBJECT_ID('tempdb.dbo.##ALL_StableColumns', 'U') IS NOT NULL DROP TABLE ##ALL_StableColumns;   SELECT @SQL_MainStableColumnTable       = 'SELECT xxx_ID_xxx = ROW_NUMBER() OVER (ORDER BY ' + @ListOfColumns_Stable + '), ' + @ListOfColumns_Stable                                             + ' INTO ##ALL_StableColumns '                                             + ' FROM (SELECT DISTINCT' + @ListOfColumns_Stable + ' FROM  ' + @TableName                                             + ' WHERE ' + (SELECT [ColumnName] FROM @StabPos_TAB WHERE [StabPos_ID] = @StabPos_ID) + ' IS NOT NULL ';                                             SELECT @StabPos_ID = @StabPos_ID + 1;             WHILE @StabPos_ID <= (SELECT MAX([StabPos_ID]) FROM @StabPos_TAB)             BEGIN             SELECT @SQL_MainStableColumnTable = @SQL_MainStableColumnTable + 'AND ' + (SELECT [ColumnName] FROM @StabPos_TAB WHERE [StabPos_ID] = @StabPos_ID) +  ' IS NOT NULL ';             SELECT @StabPos_ID = @StabPos_ID + 1;             END  SELECT @SQL_MainStableColumnTable    = @SQL_MainStableColumnTable + ' )x';  EXECUTE SP_EXECUTESQL  @SQL_MainStableColumnTable;  --####################################################################################################################### --###| Step 5 - Preparing table with all options ID --#######################################################################################################################  DECLARE @FULL_SQL_1 NVARCHAR(MAX) SELECT @FULL_SQL_1 = ''  DECLARE @i smallint  IF OBJECT_ID('tempdb.dbo.##FinalTab', 'U') IS NOT NULL DROP TABLE ##FinalTab;   SELECT @FULL_SQL_1 = 'SELECT t.*, dim.[xxx_ID_xxx] '                                     + ' INTO ##FinalTab '                                     +   'FROM ' + @TableName + ' t '                                     +   'JOIN ##ALL_Dimentions dim '                                     +   'ON t.' + (SELECT [ColumnName] FROM @DIM_TAB WHERE [DIM_ID] = 1) + ' = dim.' + (SELECT [ColumnName] FROM @DIM_TAB WHERE [DIM_ID] = 1);                                 SELECT @i = 2                                                                WHILE @i <= (SELECT MAX([DIM_ID]) FROM @DIM_TAB)                                     BEGIN                                     SELECT @FULL_SQL_1 = @FULL_SQL_1 + ' AND t.' + (SELECT [ColumnName] FROM @DIM_TAB WHERE [DIM_ID] = @i) + ' = dim.' + (SELECT [ColumnName] FROM @DIM_TAB WHERE [DIM_ID] = @i)                                     SELECT @i = @i +1                                 END EXECUTE SP_EXECUTESQL @FULL_SQL_1  --####################################################################################################################### --###| Step 6 - Selecting final data --####################################################################################################################### DECLARE @STAB_TAB TABLE ([STAB_ID] smallint, [ColumnName] nvarchar(128)) INSERT INTO @STAB_TAB  SELECT [STAB_ID] = ROW_NUMBER() OVER(ORDER BY [ColumnName]), [ColumnName] FROM #ColumnListWithActions WHERE [Action] = 'S';  DECLARE @VAR_TAB TABLE ([VAR_ID] smallint, [ColumnName] nvarchar(128)) INSERT INTO @VAR_TAB  SELECT [VAR_ID] = ROW_NUMBER() OVER(ORDER BY [ColumnName]), [ColumnName] FROM #ColumnListWithActions WHERE [Action] = 'V';  DECLARE @y smallint; DECLARE @x smallint; DECLARE @z smallint;   DECLARE @FinalCode nvarchar(max)  SELECT @FinalCode = ' SELECT ID1.*'                                         SELECT @y = 1                                         WHILE @y <= (SELECT MAX([xxx_ID_xxx]) FROM ##FinalTab)                                             BEGIN                                                 SELECT @z = 1                                                 WHILE @z <= (SELECT MAX([VAR_ID]) FROM @VAR_TAB)                                                     BEGIN                                                         SELECT @FinalCode = @FinalCode +    ', [ID' + CAST((@y) as varchar(10)) + '.' + (SELECT [ColumnName] FROM @VAR_TAB WHERE [VAR_ID] = @z) + '] =  ID' + CAST((@y + 1) as varchar(10)) + '.' + (SELECT [ColumnName] FROM @VAR_TAB WHERE [VAR_ID] = @z)                                                         SELECT @z = @z + 1                                                     END                                                     SELECT @y = @y + 1                                                 END         SELECT @FinalCode = @FinalCode +                                          ' FROM ( SELECT * FROM ##ALL_StableColumns)ID1';                                         SELECT @y = 1                                         WHILE @y <= (SELECT MAX([xxx_ID_xxx]) FROM ##FinalTab)                                         BEGIN                                             SELECT @x = 1                                             SELECT @FinalCode = @FinalCode                                                                                  + ' LEFT JOIN (SELECT ' +  @ListOfColumns_Stable + ' , ' + @ListOfColumns_Variable                                                                                  + ' FROM ##FinalTab WHERE [xxx_ID_xxx] = '                                                                                  + CAST(@y as varchar(10)) + ' )ID' + CAST((@y + 1) as varchar(10))                                                                                   + ' ON 1 = 1'                                                                                  WHILE @x <= (SELECT MAX([STAB_ID]) FROM @STAB_TAB)                                                                                 BEGIN                                                                                     SELECT @FinalCode = @FinalCode + ' AND ID1.' + (SELECT [ColumnName] FROM @STAB_TAB WHERE [STAB_ID] = @x) + ' = ID' + CAST((@y+1) as varchar(10)) + '.' + (SELECT [ColumnName] FROM @STAB_TAB WHERE [STAB_ID] = @x)                                                                                     SELECT @x = @x +1                                                                                 END                                             SELECT @y = @y + 1                                         END  SELECT * FROM ##ALL_Dimentions; EXECUTE SP_EXECUTESQL @FinalCode; 

From executing the first query (by passing source DB and table name) you will get a pre-created execution query for the second SP, all you have to do is define is the column from your source: + Stable + Value (will be used to concentrate values based on that) + Dim (column you want to use to pivot by)

Names and datatypes will be defined automatically!

I cant recommend it for any production environments but does the job for adhoc BI requests.