FIX: Number of rows is underestimated for a query predicate that involves a scalar user-defined function in SQL Server 2014

Прилага се за: SQL Server 2014 DeveloperSQL Server 2014 DeveloperSQL Server 2014 Enterprise


Consider the following scenario:

  • You have a query that contains a predicate that involves a parameterized scalar user-defined function.
  • There are multiple combinations of input parameter values that may produce the same result by this user-defined function.
  • SQL Server uses the New Cardinality Estimator in which the database compatibility mode is set to 120.

In this scenario, when you run the query, you experience poor query performance because of an incorrectly estimated number of rows for the predicate that involves the user-defined function in the query plan.


This problem was first fixed in the following cumulative update for SQL Server:

After you install this cumulative update package, you have to enable trace flag 4199. To do this, you can add the -T4199 startup parameter. Or, you can use the dbcc traceon(4199) statement for a specific session.


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


Learn about the terminology Microsoft uses to describe software updates.