How Can I Join SQL Server Tables Based on Row Number and Control Ordering?

Joining Tables on Row Number in SQL Server

In SQL Server 2008, you can perform an inner join on row number using the ROW_NUMBER() function. This function assigns a unique sequential number to each row in a table, based on an optional sorting specification.

Query for Vertically Ordering Joined Rows:

To join tables A and B on their row numbers and maintain the vertical ordering of the rows, use the following query:

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;

Query for Horizontally Ordering Joined Rows:

If you want to join the rows horizontally, without sorting, replace the ORDER BY clauses with the PARTITION BY clause:

SELECT A.val, B.val
FROM (
    SELECT val, ROW_NUMBER() OVER (PARTITION BY 1) AS row_num
    FROM A
) AS A
JOIN (
    SELECT val, ROW_NUMBER() OVER (PARTITION BY 1) AS row_num
    FROM B
) AS B
ON A.row_num = B.row_num;

Example:

Using the sample tables A and B provided, the first query will produce the following output:

RowA Row1
RowB Row2
RowC Row3
RowD Row4

The second query will produce this output, representing a horizontal join:

RowA Row4
RowB Row3
RowC Row2
RowD Row1

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