FIX: Scalar UDF Inlining issues in SQL Server 2019

Applies to: SQL Server 2019 on LinuxSQL Server 2019 on Windows


User-Defined Functions (UDFs) that are implemented inTransact-SQL and that returned a single data value are referred to as T-SQL ScalarUser-Defined Functions (UDFs). 

Microsoft SQL Server 2019 introduces the Scalar UDFInlining feature that can improve the performance of queries that invoke T-SQLScalar UDFs, where UDF execution is the main bottleneck. T-SQL Scalar UDF Inlining automatically transforms inline-able UDFs into relational expressions. 

This cumulative update includes several fixes across thefollowing areas for scenarios in which a query that uses Scalar UDF Inlining mayreturn an error or unexpected results:
  • Type mismatch error if the return type of the UDF is sql_variant (added in Microsoft SQL Server 2019 CU2) 
  • UDF invocation from sp_executesql aborts execution (added in Microsoft SQL Server 2019 CU2)
  • UDFs referencing labels without an associated GOTO command return incorrect results (added in Microsoft SQL Server 2019 CU2)
  • Out-of-memory conditions and memory leaks because of very large scalar UDFs (added in Microsoft SQL Server 2019 CU2)
  • Uninitialized variables used in condition (IF-ELSE) statements cause errors (added in Microsoft SQL Server 2019 CU2)
This cumulativeupdate also blocks Inlining in the following scenarios:
  • If the UDF references certain intrinsic functions (e.g. @@ROWCOUNT) that may alter the results when inlined (added in Microsoft SQL Server 2019 CU2)
  • Aggregate functions being passed as parameters to a scalar UDF (added in Microsoft SQL Server 2019 CU2)
  • If the UDF references built-in views (for example: OBJECT_ID) (added in Microsoft SQL Server 2019 CU2)
  • If the UDF uses XML methods (added in Microsoft SQL Server 2019 CU4)
  • If the UDF contains a SELECT with ORDER BY without a "TOP 1" (added in Microsoft SQL Server 2019 CU4)
  • If the SELECT query performs an assignment in conjunction with the ORDER BY clause (e.g. SELECT @x = @x +1 FROM table ORDER BY column_name) (added in Microsoft SQL Server 2019 CU4)
After you upgrade to Microsoft SQL Server 2019 CU2 or later, to re-evaluate whether a UDF iseligible for inlining, refresh eligible scalar UDFs through either one of thefollowing methods:
The following scriptgenerates a script to refresh metadata for existing inlined scalar UDFs:
      Generates a script that can be used to refresh all active inlineable ScalarUDFs.
      Note: sp_refreshsqlmodule does not affect any permissions, extended properties,
      or SET options that are associated with the object.
SELECT 'EXECUTEsys.sp_refreshsqlmodule ''[' + OBJECT_SCHEMA_NAME(object_id) + +'].' + '[' + OBJECT_NAME(object_id)
      + ']'';' AS 'RefreshStatement'
FROM sys.sql_modules
WHERE is_inlineable = 1
     AND inline_type = 1;


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


This issue is fixed in the following cumulative update for SQL Server:
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