How Can I Use ROW_NUMBER() Without ORDER BY in SQL Server 2005?

ROW_NUMBER() without ORDER BY in SQL Server 2005

In SQL Server 2005, the ROW_NUMBER() function can be used to generate a unique sequential number for each row in a result set. However, unlike its counterparts in later versions, ROW_NUMBER() in SQL Server 2005 requires an explicit ORDER BY clause. This limitation poses a challenge when attempting to generate sequential numbers without altering the original order of the data.

Solution:

To work around this limitation, we can avoid specifying an explicit ordering using the following query syntax:

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

Explanation:

• The outermost ORDER BY (SELECT 1) serves as a placeholder, effectively avoiding any explicit ordering.
• The WITH (TABLOCKX, HOLDLOCK) hints are used to prevent concurrency issues by ensuring exclusive table locks.

Considerations:

• This workaround does not guarantee that the original order of the data will be preserved. Other factors, such as locks and concurrent processes, can affect the resulting order.
• It is not as efficient as using an identity column for auto-incrementing.
• Using an identity column is the preferred solution for concurrency and performance reasons.

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