How Can I Auto-Increment a Non-Identity Column in SQL Server 2005 Using ROW_NUMBER()?

Using ROW_NUMBER() without ORDER BY for Auto-Incrementing in SQL Server 2005

In SQL Server 2005, auto-incrementing a non-identity column can be challenging when working with ROW_NUMBER() and a lack of a suitable ORDER BY criterion. However, there are alternatives:

Using ROW_NUMBER() with a Constant Order By Clause:

Although lacking a valid ORDER BY field, ROW_NUMBER() can be combined with a constant ordering clause to mimic auto-incrementing:

INSERT dbo.TargetTable (ID, FIELD)
SELECT
   Row_Number() OVER (ORDER BY (SELECT 1))
      + Coalesce(
         (SELECT Max(ID) FROM dbo.TargetTable WITH (TABLOCKX, HOLDLOCK)),
         0
      ),
   FieldValue
FROM dbo.SourceTable
WHERE {somecondition};

This method avoids explicit ordering while ensuring uniqueness in the ID column.

Caveat: Non-Guarantee of Original Ordering:

It's crucial to note that this approach does not guarantee the preservation of the original SourceTable order. Other factors, such as an outer query's ORDER BY, can influence the result ordering.

Considerations for Concurrency:

Locking hints (TABLOCKX and HOLDLOCK) are included in the query to prevent concurrent processes from inserting the same ID between query execution steps. However, this approach is not as efficient as using an identity column and should only be considered a workaround.

Recommended Solution: Use Identity Column:

For optimal performance and concurrency, it is strongly recommended to use an identity column for auto-incrementing.

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