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[SOLVED] Efficiently convert rows to columns in sql server

By tbag

2013-04-01 14:11:17 8 Comments

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?

2 comments

@Taryn 2013-04-01 14:13:33

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'

@Gordon Linoff 2013-04-01 14:29:47

+1 . . . But in the last example, you can use cross join rather than left join because each subquery returns one row.

@tbag 2013-04-01 14:32:26

I need to build a dynamic query because I don't know the number of rows. Lets talk about converting a table with 10.000.000 millions of records

@Taryn 2013-04-01 14:33:41

@tbag If you have an unknown number of rows, then you would have to use dynamic sql but be aware that transforming millions of rows will not be efficient.

@tbag 2013-04-01 14:37:09

I can't use a view for that transformation, what about using a TFV? that's why I'm looking for an efficient solution.

@Taryn 2013-04-01 14:39:06

@tbag Dynamic SQL cannot be used in a view or a table valued function, it must be used in a stored procedure

@tbag 2013-04-01 14:58:54

Suppose that I need to convert my rows into columns, I should convert it to a stored procedure, but in that case, I can't use it as a main table for running queries... is there any other way?

@Taryn 2013-04-01 15:01:01

@tbag Well that is a different question, what exactly are you going to want to JOIN on once this is transposed? You could create a temp table that has this data loaded into it and then you can use the join in your joins.

@tbag 2013-04-01 15:18:19

I want to convert my rows into columns an then use it in queries, before I was using the cases with max() in a view, now I would like to replace it for something better}.

@tbag 2013-04-01 15:20:46

what is exactly doing this: .value('.', 'NVARCHAR(MAX)') in your previous query? thanks!

@Taryn 2013-04-01 15:21:17

@tbag Unfortunately if you want to use dynamic sql then you will have to use a stored procedure, then if you need to join on the result you will have to load the data into a table for use.

@Taryn 2013-04-01 15:22:06

@tbag this code .value('.', 'NVARCHAR(MAX)') is used with the stuff function and for xml path to get the list of values to be converted to columns.

@Haminteu 2014-08-07 04:58:30

@bluefeet, Well this is a good one. I've a question. In the first syntax of your answer, I tried that... But with 20 records, why its only show 1 - 5 records only?

@Taryn 2014-08-07 11:04:50

@Haminteu If you are pivoting a string and you have multiple rows for each item you are grouping by, then you'll need to use row_number() to return multiple rows. Check out this answer to see what I mean.

@devinbost 2014-09-06 20:09:57

You want a clue? Try creating a function that generates the statement and using a cross-apply to apply it to all of your values.

@navbingo 2014-12-15 02:46:51

@bluefeet i am having the same table structure, and i used the 2nd solution as suggested above [Dynamic solution].. when i execute it , it returning me error : The column 'id' was specified multiple times for 'p'.

@Beytan Kurt 2017-02-13 09:14:51

remember to cover column names with brackets in pivot statement.

@xyzabc 2019-01-30 07:45:44

Is there a way to use above aggregate function example with unknown number of columns? or can someone suggest me a way to do above same thing using oracle

@Taryn 2019-01-30 12:54:10

@xyzabc Yes, it can be done in Oracle - here is another answer I wrote with how to do it. I haven't worked with Oracle in years, so there might be better ways to do it now.

@hoggar 2019-04-06 15:20:53

@Taryn If I have dots in columnname column then I got error message: "The multi-part identifier "First.Last" could not be bound."

@Taryn 2019-04-06 15:22:40

@hoggar You'll need to escape the dot by using square brackets [First.Last]

@Bartosz X 2017-01-23 16:01:02

as pivoting data is still a hot one I decided to add something form me. This is rather a method than just a single script but gives you much more possibilities. First of all There are 3 scripts you need to deploy: 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](128) NOT NULL,
        [Action] [nchar](1) NOT NULL
    );
GO

    CREATE PROCEDURE [dbo].[proc_PivotPrepare] 
    (
    @DB_Name        nvarchar(128),
    @TableName      nvarchar(128)
    )
    AS
    ----------------------------------------------------------------------------------------------------
    -----| Author: Bartosz
    ----------------------------------------------------------------------------------------------------
    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].[proc_PivotExecute]
(
@ColumnListWithActions  ColumnActionList ReadOnly
,@TableName                     nvarchar(128)
)
AS
--#######################################################################################################################
--###| Author: Bartosz
--#######################################################################################################################


--#######################################################################################################################
--###| 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 ID = 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 ID = 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.[ID] '
                                    + ' 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([ID]) 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([ID]) FROM ##FinalTab)
                                        BEGIN
                                            SELECT @x = 1
                                            SELECT @FinalCode = @FinalCode 
                                                                                + ' LEFT JOIN (SELECT ' +  @ListOfColumns_Stable + ' , ' + @ListOfColumns_Variable 
                                                                                + ' FROM ##FinalTab WHERE [ID] = ' 
                                                                                + 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.

@FAB 2018-09-19 16:10:11

All good until Could not find stored procedure 'dbo.sp_PivotIt'. Any advice?

@Bartosz X 2018-09-24 14:02:55

@DarXyde sory I must mixed 2 versions, please recompile and try again

@FAB 2018-09-25 18:35:40

Thanks Bartosz, managed to use some of the ideas from your script and done what I had on my mind already, but nevertheless, thanks for updating it :) . I should have thought to change that line, but honestly thought is a stored procedure you've forgot is not default in the system or something like that. I will give it a run when i get close to that project again, and update here!

@FAB 2018-09-26 10:02:03

Still the wrong name of the SP, but now that i know what's wrong, easy to fix: sp_Pivot_Execute change to proc_PivotExecute.

@Bartosz X 2018-09-26 10:36:31

@DarXyde - thanks, for spotting that - this has now been fixed

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