


How Does Row Order Differ Between SQL Server 2008 and SQL Server 2012 SELECT Queries?
Jan 14, 2025 am 10:52 AMSQL Server 2008 vs. 2012: SELECT Query Row Order Discrepancies
The Problem:
Upgrading from SQL Server 2008 to SQL Server 2012 has revealed a critical difference: the default row order in SELECT
queries without an ORDER BY
clause. While SQL Server 2008 often returned rows in a seemingly consistent order, SQL Server 2012 provides no such guarantee.
The Impact:
This change significantly affects applications relying on this implicit ordering, particularly impacting over 2500 stored procedures across 5 databases. A blanket addition of ORDER BY
clauses is impractical. Developers are seeking efficient solutions, even considering a downgrade to SQL Server 2008.
Why Explicit Ordering is Essential:
Downgrading is not recommended. The expectation of a default row order is fundamentally flawed. SQL operates on sets, and sets inherently lack inherent order. As Itzik Ben-Gan highlights in "Microsoft SQL Server 2012 T-SQL Fundamentals," query results are unordered unless explicitly sorted.
The Unpredictability of Implicit Order:
Developers must always use explicit ORDER BY
clauses. The query optimizer might rearrange operations for performance, potentially altering any perceived default order.
Best Practices for Consistent Row Order:
To ensure predictable results:
-
Always include
ORDER BY
inSELECT
statements where row order is relevant. - If the default order is critical, create an index enforcing that order.
- Note that even with
ORDER BY
, order might vary across different query plans, especially with parallel execution.
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