Microsoft® SQL Server 2012 Unleashed

Automatic Query Plan Recompilation

SQL Server attempts to reuse existing execution plans for stored procedures, but certain operations cause the execution plans to become inefficient or invalid. In these cases, a new execution plan needs to be recompiled on the next execution of the stored procedure. The following conditions cause a plan to be invalidated:

Whenever there is a change to the schema of a referenced table or view

When an index for a referenced table is dropped or changed

When the statistics used by an execution plan have been updated, ...