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
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Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.