How to Perform an Inner Join Based on Row Numbers in SQL Server?

How to Perform an Inner Join on Row Number in SQL Server

In the realm of SQL Server programming, the question of how to perform an inner join on row number often arises. This article explores the topic and provides solutions to help you achieve the desired results.

To illustrate the challenge, consider two tables, A and B, each containing a list of values ordered from top to bottom:

• Table A: RowA, RowB, RowC, RowD
• Table B: Row4, Row3, Row2, Row1

The objective is to perform an inner join on the two tables, matching rows based on their row numbers. By default, SQL Server does not provide a native way to join tables on row numbers. However, using the ROW_NUMBER() function, we can create a virtual column that assigns a unique row number to each row in each table.

To perform an inner join on row numbers in SQL Server 2008, you can use the following steps:

-- Create a virtual column with row numbers for Table A
SELECT val, ROW_NUMBER() OVER (ORDER BY val) AS row_num
FROM A

-- Create a virtual column with row numbers for Table B
SELECT val, ROW_NUMBER() OVER (ORDER BY val) AS row_num
FROM B

-- Join the two tables on the row number virtual columns
SELECT A.val, B.val
FROM (
  SELECT val, row_num
  FROM A
) AS A
INNER JOIN (
  SELECT val, row_num
  FROM B
) AS B
ON A.row_num = B.row_num
ORDER BY A.val, B.val

This query will return the following output:

• RowA Row1
• RowB Row2
• RowC Row3
• RowD Row4

By matching the row numbers, we have successfully inner joined the two tables.

Alternatively, if you do not have a specific order-by requirement, you can achieve the same result without explicitly ordering the tables:

-- Create a virtual column with row numbers for Table A
SELECT val, ROW_NUMBER() OVER () AS row_num
FROM A

-- Create a virtual column with row numbers for Table B
SELECT val, ROW_NUMBER() OVER () AS row_num
FROM B

-- Join the two tables on the row number virtual columns
SELECT A.val, B.val
FROM (
  SELECT val, row_num
  FROM A
) AS A
INNER JOIN (
  SELECT val, row_num
  FROM B
) AS B
ON A.row_num = B.row_num
ORDER BY A.row_num

This query will return the rows in the order they come out:

• RowA Row4
• RowB Row3
• RowC Row2
• RowD Row1

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