How Does the SQL Server 2012 Upgrade Affect Row Order in SELECT Queries Without ORDER BY?

SQL Server 2012: Row Order Changes in SELECT Queries

SQL Server 2012 significantly alters how row order is handled in SELECT statements lacking an explicit ORDER BY clause. Unlike its predecessor, SQL Server 2008, which implicitly guaranteed a specific row order, SQL Server 2012 offers no such guarantee. The order of returned rows becomes unpredictable without an ORDER BY clause.

Impact on Existing Applications

This change directly impacts applications relying on consistent row ordering. For example, over 2500 stored procedures across 5 databases require updates to maintain predictable results.

Solutions

1. Implement ORDER BY Clauses:

The recommended solution is to add appropriate ORDER BY clauses to all affected stored procedures. While labor-intensive, this guarantees consistent row order and prevents unexpected query outcomes.

2. Downgrading (Not Recommended):

Reverting to SQL Server 2008 restores the previous implicit ordering. However, this is strongly discouraged due to the complexities and potential support issues involved.

SQL, Set Theory, and Row Order

SQL's inherent lack of row order stems from its foundation in set theory. Sets, by definition, have no inherent ordering. Therefore, the order of rows in a SQL result set is, fundamentally, arbitrary.

SQL Server's Historical Behavior and Current Best Practices

While previous SQL Server versions sometimes implied order, this was undocumented and unreliable. Numerous blog posts and expert advice caution against relying on this implicit behavior. The query optimizer team has explicitly advised against it.

Conclusion

The shift in row order behavior in SQL Server 2012 necessitates the use of ORDER BY clauses in all applications requiring predictable row sequencing. While demanding significant effort, this is crucial for data integrity and consistent query results.

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