ROW_NUMBER in SQL Server: Purpose & Use

In SQL Server, the ROW_NUMBER function is used to assign a unique consecutive number to each row in the result set.

The ROW_NUMBER function is commonly used in the following scenarios:

1. Pagination query: You can achieve pagination functionality by using the value of ROW_NUMBER, for example, selecting data based on the value of ROW_NUMBER for a specific page.
2. Sorting: The result set can be sorted based on the value of ROW_NUMBER, such as arranging in ascending or descending order based on a specific field.
3. Remove duplicates: We can use the ROW_NUMBER function to eliminate duplicate rows from the result set, such as by numbering the duplicate rows using the ROW_NUMBER function and keeping one of them.

The basic syntax of the ROW_NUMBER function is as follows:

ROW_NUMBER() OVER (PARTITION BY column ORDER BY expression [ASC|DESC])

1. The PARTITION BY clause is optional and is used to specify the columns for partitioning. If not specified, the numbering is done over the entire result set.
2. ORDER BY is used to specify the column for sorting, if not specified, the data will be numbered in its original order.
3. ASC | DESC: Optional item that specifies the order of sorting, with the default being ascending.

Note: The ROW_NUMBER function assigns a unique consecutive number to each row in the result set, but does not actually sort or filter the result set.