When you run a query in Microsoft SQL Server 2012 or SQL Server 2014, and the following conditions are true, a suboptimal execution plan is generated in SQL Server 2012:
- The query contains a Case, When, Then, and Else statement.
- The When statement has a constant condition that evaluates to "false".
- The Then statement contains a Select clause.
- In the execution plan, the Then statement is evaluated and compared to isFalseOrNull(0). However, the When statement always evaluates to "false".
- This issue does not occur in Microsoft SQL Server 2008 R2
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.