How Does Default Row Ordering Differ Between SQL Server 2008 and SQL Server 2012 SELECT Queries?

Differences in default row ordering in SELECT queries between SQL Server 2008 and SQL Server 2012

The lack of an explicit ORDER BY clause in a SQL query raises concerns about default row ordering, especially when upgrading from SQL Server 2008 to SQL Server 2012. While SQL Server 2012 guarantees no specific ordering without an ORDER BY clause, this was not made clear in earlier versions, leading to the mistaken belief that ordering in SQL Server 2008 is consistent.

Understand set theory and SQL result sorting

To understand row ordering, you must understand the role of set theory in SQL. According to set theory, the results of a SELECT query constitute a set or multiset, where the elements (rows) are distinct objects. Crucially, there is no inherent ordering of collection elements, and the same applies to SQL results.

Reliability of row sorting without ORDER BY

Relying on row order without explicit ordering is unreliable. Result sets in SQL never will have guaranteed ordering without using ORDER BY.

Avoid potential pitfalls

To ensure consistent ordering, the desired order must be explicitly declared using ORDER BY. Inconsistent sorting observed after upgrading to SQL Server 2012 may be due to changes in hardware configuration, data storage arrangements, and query optimizer behavior.

Solution

The recommended solution is to manually add the ORDER BY clause to all affected stored procedures. Downgrading to SQL Server 2008 is not recommended due to the inherent lack of ordering guarantees and the fact that there are no errors in the upgrade itself.

Other notes

Various Microsoft resources emphasize the importance of using ORDER BY to maintain consistent row ordering. Failure to do so may result in unexpected or incorrect results.

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