Overview of the SQL ROW_NUMBER function

 

ROW_NUMBER() is a function in SQL Server that assigns a unique number to each row within a result set, based on the order specified in the ORDER BY clause of the ROW_NUMBER() function. The function is typically used in conjunction with the SELECT statement and is commonly used for pagination, ranking, and other types of data analysis. The syntax for using the ROW_NUMBER() function is as follows:

SELECT ROW_NUMBER() OVER (ORDER BY column_name) as row_number, column1, column2, ...

FROM table_name

The OVER clause is used to define the window or partition of the result set to which the ROW_NUMBER() function applies, and the ORDER BY clause is used to specify the order in which the row numbers are assigned. The ROW_NUMBER() function can also be used with the PARTITION BY clause to generate unique numbers for each partition of the result set.

SELECT ROW_NUMBER() OVER (PARTITION BY column1 ORDER BY column2) as row_number, column1, column2, ... 

FROM table_name

This will assign unique numbers to each rows within the same partition.

 

Here are some examples of using ROW_NUMBER() in SQL Server:

1.       Assign a unique number to each row in a result set:

SELECT ROW_NUMBER() OVER (ORDER BY column1) as RowNumber, column1, column2

FROM table_name

2.       Assign a unique number to each row within a group:

SELECT ROW_NUMBER() OVER (PARTITION BY column1 ORDER BY column2) as RowNumber, column1, column2

FROM table_name

3.       Assign a unique number to each row within a group, and also include a custom prefix:

SELECT 'PREFIX_' + CAST(ROW_NUMBER() OVER (PARTITION BY column1 ORDER BY column2) as varchar(10)) as RowNumber, column1, column2

FROM table_name

4.       Assign a unique number to each row within a group, and also include a custom prefix and reset the numbering for each group:

SELECT column1, 'PREFIX_' + CAST(ROW_NUMBER() OVER (PARTITION BY column1 ORDER BY column2) as varchar(10)) as RowNumber, column2

FROM table_name

5.       Finding duplicate rows: By assigning a unique number to each row based on the columns that you want to check for duplicates, you can filter out duplicate rows.

WITH CTE AS (

    SELECT column1, column2, ROW_NUMBER() OVER (PARTITION BY column1, column2 ORDER BY column1) as row_number

    FROM table_name

)

SELECT column1, column2

FROM CTE

WHERE row_number = 1;

This query will return only one row for each set of duplicate values of column1 and column2.

 6.       Generating running totals: By using the ROW_NUMBER() function in conjunction with the SUM() function, you can generate a running total for a specific column.

WITH CTE AS (

    SELECT column1, column2, ROW_NUMBER() OVER (ORDER BY column1) as row_number,

    SUM(column2) OVER (ORDER BY column1) as running_total

    FROM table_name

)

SELECT column1, column2, running_total

FROM CTE;

This query will return the column1,column2 and the running total of column2 in the order of column1

 7.       Generating a unique row number for each group of data: By using the ROW_NUMBER() function in conjunction with the GROUP BY clause, you can generate a unique row number for each group of data.

SELECT column1, column2, ROW_NUMBER() OVER (PARTITION BY column1 ORDER BY column2) as row_number

FROM table_name

GROUP BY column1, column2;

This query will return the column1, column2 and the unique row number for each group of column1

 8.       Filtering out a specific range of rows: By using the ROW_NUMBER() function in conjunction with the WHERE clause, you can filter out a specific range of rows based on the unique number assigned to each row.

WITH CTE AS (

    SELECT column1, column2, ROW_NUMBER() OVER (ORDER BY column1) as row_number

    FROM table_name

)

SELECT column1, column2

FROM CTE

WHERE row_number BETWEEN 5 AND 10;

9.       Generating a running average: By using the ROW_NUMBER() function in conjunction with the AVG() function and a CTE, you can generate a running average for a specific column.

WITH CTE AS (

    SELECT column1, column2, ROW_NUMBER() OVER (ORDER BY column1) as row_number,

    AVG(column2) OVER (ORDER BY column1 ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW) as running_average

    FROM table_name

)

SELECT column1, column2, running_average

FROM CTE;

10.   Extracting a specific number of rows from a query: By using the ROW_NUMBER() function in conjunction with the TOP clause, you can extract a specific number of rows from a query.

WITH CTE AS (

    SELECT TOP 100 ROW_NUMBER() OVER (ORDER BY column1) as row_number, column1, column2

    FROM table_name

)

SELECT column1, column2

FROM CTE;

11.   Filtering out the top N rows based on a specific column: By using the ROW_NUMBER() function in conjunction with the TOP clause and the ORDER BY clause, you can filter out the top N rows based on the values of a specific column.

WITH CTE AS (

    SELECT TOP 10 ROW_NUMBER() OVER (ORDER BY column1 DESC) as row_number, column1, column2

    FROM table_name

)

SELECT column1, column2

FROM CTE

WHERE row_number = 1;

12.   Generating a cumulative sum: By using the ROW_NUMBER() function in conjunction with the SUM() function, you can generate a cumulative sum for a specific column.

WITH CTE AS (

    SELECT column1, column2, ROW_NUMBER() OVER (ORDER BY column1) as row_number,

    SUM(column2) OVER (ORDER BY column1 ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW) as cumulative_sum

    FROM table_name

)

SELECT column1, column2, cumulative_sum

FROM CTE;

13.   Generating a running maximum: By using the ROW_NUMBER() function in conjunction with the MAX() function, you can generate a running maximum for a specific column.

WITH CTE AS (

    SELECT column1, column2, ROW_NUMBER() OVER (ORDER BY column1) as row_number,

    MAX(column2) OVER (ORDER BY column1 ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW) as running_max

    FROM table_name

)

SELECT column1, column2, running_max

FROM CTE;

14.   Randomly selecting a specific number of rows from a table: By using the ROW_NUMBER() function in conjunction with the NEWID() function, you can randomly select a specific number of rows from a table.

WITH CTE AS (

    SELECT column1, column2, ROW_NUMBER() OVER (ORDER BY NEWID()) as row_number

    FROM table_name

)

SELECT column1, column2

FROM CTE

WHERE row_number BETWEEN 1 AND 100;

15.   Generating a running median: By using the ROW_NUMBER() function in conjunction with the NTILE() function, you can generate a running median for a specific column.

WITH CTE AS (

    SELECT column1, column2, ROW_NUMBER() OVER (ORDER BY column1) as row_number,

    )

SELECT column1, column2, median

FROM CTE;

NTILE(2) OVER (ORDER BY column2) as median

FROM table_name

16.   Generating a running standard deviation: By using the ROW_NUMBER() function in conjunction with the STDEV() function, you can generate a running standard deviation for a specific column.

WITH CTE AS (

    SELECT column1, column2, ROW_NUMBER() OVER (ORDER BY column1) as row_number,

    STDEV(column2) OVER (ORDER BY column1 ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW) as running_stdev

    FROM table_name

)

SELECT column1, column2, running_stdev

FROM CTE;