How Can I Duplicate SQL Result Rows and Assign Row Numbers Based on a Count Column?

Duplicating Result Rows with Row Numbering in SQL

In many database operations, it is often necessary to expand result rows and assign unique numbers to them. This technique is particularly useful when working with data that has varying row counts. For instance, consider the following data:

value | count
------+------
foo   |     1
bar   |     3
baz   |     2

To transform this data into a format where rows with counts greater than 1 are repeated and each row is assigned an index, several approaches can be taken.

Using a Numbers Table

A common solution is to utilize a join operation with a numbers table. This table contains a sequence of numbers that can be used to generate the desired indexing.

SELECT value, count, number
FROM table
JOIN Numbers
    ON table.count >= Numbers.number

This method generates the desired output for all major databases, including Oracle, SQL Server, MySQL, and PostgreSQL.

Example Implementation (SQL Server)

WITH N AS (SELECT ROW_NUMBER() OVER (ORDER BY object_id) AS number
              FROM sys.objects)
SELECT value, count, number
FROM table
JOIN N
    ON table.count >= N.number;

This modified query utilizes a common table expression (CTE) named "N" to create a numbers table and achieve the desired output.

Database-Specific Considerations

Although the above solution is cross-database compatible, there may be more database-specific approaches that provide additional optimizations or performance benefits. It is recommended to explore such options for specific database environments.

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