Convert Rows To Columns In SQL Server Using Dynamic Pivot

convert rows to columns in sql server

In this article, we will explain how to Convert Rows To Columns In SQL Server Using Dynamic Pivot step by step.

Applies To

  • SQL Server 2017.
  • SQL Server 2016.
  • SQL Server 2012.
  • SQL Server 2008.

You might also like to read Dynamic pivot without aggregate function in SQL Server


Using Dynamic Pivot to Convert Rows To Columns In SQL Server

We have decided to build a dynamic database by creating only three tables as shown below:

Convert Rows To Columns In SQL Server
  • The “Tables” will be used to hold the table names like Users, Products….etc.
Tables - convert rows to columns using Dynamic Pivot in SQL Server
  • The “Fields” will be used to hold the fields name related to each table.
convert rows to columns using Dynamic Pivot in SQL Server
  • The “Field Value” will be used to hold the value of each field.
Field Values - convert rows to columns using Dynamic Pivot in SQL Server
  • The relationship between the three tables is one-many and the ERD looks like the below:
convert rows to columns using Dynamic Pivot in SQL Server

The desired data should look like:

Dynamic Pivot In SQL Server

PIVOT rotates a table-valued expression by turning the unique values from one column in the expression into multiple columns in the output and performs aggregations where they are required on any remaining column values that are wanted in the final output.


How to Convert Rows To Columns In SQL?

To Convert Rows To Columns In SQL, we will go through the following steps:

  1. Get a list of the Field Values (Rows).
  2. Get a list of the Fields (Columns).
  3. Build the Dynamic Pivot Table Query

Get a list of the Field Values (Rows)

In this section, we will get a list of “field values” that should be shown as rows by doing the following:

Steps

  • Create a table “data-query” that will hold the field data values.
BEGIN try 
    DROP TABLE ##dataquery 
END try 

BEGIN catch 
END catch 

CREATE TABLE ##dataquery 
  ( 
     id         INT NOT NULL, 
     tablename  VARCHAR(50) NOT NULL, 
     fieldname  VARCHAR(50) NOT NULL, 
     fieldvalue VARCHAR(50) NOT NULL 
  ); 
  • Query the field values data filtered by “TableID” and insert the output into the created table in the above step.
INSERT INTO ##dataquery
SELECT Row_number()
         OVER (
           partition BY (fields.fieldname)
           ORDER BY fieldvalue.fieldvalue) ID,
       tables.tablename,
       fields.fieldname,
       fieldvalue.fieldvalue
FROM   tables
       INNER JOIN fields
               ON tables.tid = fields.tid
       INNER JOIN fieldvalue
               ON fields.fid = fieldvalue.fid
WHERE  tables.tid = @TableID

Output

convert rows to columns using Dynamic Pivot in SQL Server

Get a list of the Fields (Columns)

In this section, we will retrieve the list of the fields filtered by “TableID” by using the below SQL statement.

DECLARE @DynamicColumns AS VARCHAR(max)
 
SELECT @DynamicColumns = COALESCE(@DynamicColumns + ', ', '')
                         + Quotename(fieldname)
FROM   (SELECT DISTINCT fieldname
        FROM   fields
        WHERE  fields.tid = @TableID) AS FieldList

COALESCE: Evaluates the arguments in order and returns the current value of the first expression that initially does not evaluate to NULL.

Quotename: Returns a Unicode string with the delimiters added to make the input string a valid SQL Server delimited identifier.Build the Dynamic Pivot Table Query

Build the Dynamic Pivot Table Query

In this section, we will combine the above two queries to can build our Dynamic Pivot

DECLARE @FinalTableStruct AS NVARCHAR(max)
 
SET @FinalTableStruct = 'SELECT ' + @DynamicColumns +
' from ##DataQuery x pivot ( max( FieldValue ) for FieldName in (' + @DynamicColumns + ') ) p '
 
EXECUTE(@FinalTableStruct)

Output

convert rows to columns using Dynamic Pivot in SQL Server

Download Final Pivot Query to Convert Rows To Columns In SQL

Finally, the Dynamic Pivot Script should look like

DECLARE @TableID AS INT
 
SET @TableID=1 -- Set Table ID
 
-- Get a list of the "Field Value" (Rows) 
BEGIN try
    DROP TABLE ##dataquery
END try
 
BEGIN catch
END catch
 
CREATE TABLE ##dataquery
  (
     id         INT NOT NULL,
     tablename  VARCHAR(50) NOT NULL,
     fieldname  VARCHAR(50) NOT NULL,
     fieldvalue VARCHAR(50) NOT NULL
  );
 
INSERT INTO ##dataquery
SELECT Row_number()
         OVER (
           partition BY (fields.fieldname)
           ORDER BY fieldvalue.fieldvalue) ID,
       tables.tablename,
       fields.fieldname,
       fieldvalue.fieldvalue
FROM   tables
       INNER JOIN fields
               ON tables.tid = fields.tid
       INNER JOIN fieldvalue
               ON fields.fid = fieldvalue.fid
WHERE  tables.tid = @TableID
 
--Get a list of the "Fields" (Columns) 
DECLARE @DynamicColumns AS VARCHAR(max)
 
SELECT @DynamicColumns = COALESCE(@DynamicColumns + ', ', '')
                         + Quotename(fieldname)
FROM   (SELECT DISTINCT fieldname
        FROM   fields
        WHERE  fields.tid = @TableID) AS FieldList
 
--Build the Dynamic Pivot Table Query  
DECLARE @FinalTableStruct AS NVARCHAR(max)
 
SET @FinalTableStruct = 'SELECT ' + @DynamicColumns
                        +
' from ##DataQuery x pivot ( max( FieldValue ) for FieldName in ('
                        + @DynamicColumns + ') ) p '
 
EXECUTE(@FinalTableStruct)

Output

How to use Dynamic Pivot in SQL

Download the database structure and the final query to convert rows to columns in SQL from GitHub at Convert rows to columns using pivot in SQL or from TechNet Gallary.


See Also

References

Credit to me at SQL Script: Convert Rows To Columns Using Dynamic Pivot In SQL Server

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