convert columns to rows in sql server with code examples

Converting columns to rows in SQL Server can be done using the UNPIVOT operator. The UNPIVOT operator allows you to rotate data from a set of columns into a set of rows. This can be useful when you need to display data in a different format, or when you need to join data from multiple columns into a single row. In this article, we will look at examples of how to use the UNPIVOT operator in SQL Server.

The basic syntax for the UNPIVOT operator is as follows:

UNPIVOT (column_name FOR column_name_alias IN (column_1, column_2, ...))

The column_name parameter specifies the column that you want to use as the new row values. The column_name_alias parameter specifies the name of the new column that will contain the original column names. The IN clause specifies the list of columns that you want to convert to rows.

Here is an example of how to use the UNPIVOT operator to convert columns to rows:

SELECT column_name_alias, column_name
FROM table_name
UNPIVOT (column_name FOR column_name_alias IN (column_1, column_2, column_3))

In this example, we are converting the columns column_1, column_2, and column_3 to rows and using column_name_alias as the name of the new column that will contain the original column names. The result of this query will be a table with two columns: column_name_alias and column_name. The column_name_alias column will contain the names of the original columns, and the column_name column will contain the values from those columns.

You can also use the UNPIVOT operator to convert specific rows to columns. For example, you can use the following query to convert the rows with the ID values 1, 2, and 3 to columns:

SELECT column_name_alias, column_name
FROM table_name
UNPIVOT (column_name FOR column_name_alias IN (column_1, column_2, column_3))
WHERE ID IN (1, 2, 3)

In this example, we are using the WHERE clause to filter the rows that we want to convert to columns. The result of this query will be a table with two columns: column_name_alias and column_name. The column_name_alias column will contain the names of the original columns, and the column_name column will contain the values from the rows with the ID values 1, 2, and 3.

Another way to convert columns to rows in SQL Server is by using the PIVOT operator. The PIVOT operator allows you to rotate data from a set of rows into a set of columns. The basic syntax for the PIVOT operator is as follows:

PIVOT (aggregate_function(column_name) FOR column_name_alias IN (value_1, value_2, ...))

The aggregate_function parameter specifies the aggregate function that you want to use to calculate the values for the new columns. The column_name parameter specifies the column that you want to use as the values for the new columns. The column_name_alias parameter specifies the name of the new columns that will be created. The IN clause specifies the list of values that you want to use as the column headers.

Here is an example of how to use the PIVOT operator to convert columns to rows
Another related topic to converting columns to rows in SQL Server is the use of the CROSS APPLY operator. The CROSS APPLY operator allows you to join a table-valued function to a query, and it is often used in conjunction with the UNPIVOT operator. The basic syntax for the CROSS APPLY operator is as follows:

SELECT column_name
FROM table_name
CROSS APPLY function_name(parameter_name)

In this example, we are using the CROSS APPLY operator to join the results of the function_name function to the table_name table. The function_name function takes the parameter_name parameter as input, and it returns a table with one or more columns. The column_name column is a column from the table_name table, and it is included in the result set of the query.

Here's an example of using the CROSS APPLY operator and UNPIVOT to convert columns to rows

SELECT column_name_alias, column_name
FROM table_name
CROSS APPLY 
(
    SELECT column_name
    FROM
    (
        SELECT column_1, column_2, column_3
        FROM table_name
    ) AS source_table
    UNPIVOT (column_name FOR column_name_alias IN (column_1, column_2, column_3))
)

In this example, we are using a subquery inside the CROSS APPLY operator to select the columns that we want to convert to rows. The subquery is used to create a new table called source_table, which contains the columns column_1, column_2, and column_3. We then use the UNPIVOT operator to convert the columns in the source_table table to rows. The result of this query will be a table with two columns: column_name_alias and column_name. The column_name_alias column will contain the names of the original columns, and the column_name column will contain the values from those columns.

Another related topic is the use of dynamic SQL for converting columns to rows. Dynamic SQL allows you to create and execute SQL statements at runtime, which can be useful when you need to generate SQL statements based on user input or other dynamic data.

DECLARE @columns AS NVARCHAR(MAX),
        @query  AS NVARCHAR(MAX);

SET @columns = STUFF((SELECT ',' + QUOTENAME(C.name) 
                    FROM sys.columns C
                    WHERE C.object_id = OBJECT_ID('table_name')
                    FOR XML PATH(''), TYPE
                    ).value('.', 'NVARCHAR(MAX)') 
                ,1,1,'')

SET @query = 'SELECT column_name_alias, column_name FROM 
             (
                SELECT ' + @columns + ' 
                FROM table_name
             ) x
             UNPIVOT 
             (
                column_name
                FOR column_name_alias in (' + @columns + ')
             ) u'
             
EXECUTE sp_executesql @query;

In this example, we are using the sys.columns system view to retrieve the list of columns in the table_name table. We then use the STUFF function to concatenate the column names into a single string. We store

convert columns to rows in sql server with code examples

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