How Can I Join Two Tables Based on Their Row Numbers in SQL Server 2008?

Joining Tables on Row Number

Problem Statement:

You have two tables with a common feature: their row numbers. Your goal is to perform an inner join on that attribute and retrieve specific data.

Specific Scenario:

Consider two tables, A and B, with the following data:

Table A

RowA

RowB

RowC

RowD

Table B

Row4

Row3

Row2

Row1

Desired Output:

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

Solution:

To achieve the desired inner join on row number, you can utilize the ROW_NUMBER() function in SQL Server 2008 as follows:

SELECT A.val, B.val
FROM (
    SELECT val, ROW_NUMBER() OVER (ORDER BY val) AS row_num
    FROM A
) AS A
JOIN (
    SELECT val, ROW_NUMBER() OVER (ORDER BY val) AS row_num
    FROM B
) AS B
ON A.row_num = B.row_num
ORDER BY A.val, B.val

Explanation:

• The ROW_NUMBER() function assigns a sequence number to each row within a table, based on the specified ORDER BY clause.
• The join condition A.row_num = B.row_num matches rows with identical row numbers, ensuring alignment of the join on the row number attribute.
• The ORDER BY A.val, B.val clause ensures that the output rows are ordered in the sequential order of table A and table B.

Alternative Scenario:

If you require the rows to appear in the same order as they do in the individual tables without an ORDER BY clause, modify the query to:

SELECT A.val, B.val
FROM (
    SELECT val, ROW_NUMBER() OVER (ORDER BY val) AS row_num
    FROM A
) AS A
JOIN (
    SELECT val, ROW_NUMBER() OVER (ORDER BY val) AS row_num
    FROM B
) AS B
ON A.row_num = B.row_num

This revision eliminates the additional ORDER BY clause, retaining the original sequence of rows.

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