Sql-server – how to solve this warning in select

The return type of the FOR XML PATH expression is NVARCHAR(MAX), not XML.

I was being confused by the fact that SSMS renders any column named XML_F52E2B61-18A1-11d1-B105-00805F49916B as if it has the XML data type. If I run the following command, I get a clickable XML result cell in SSMS:

SELECT 'hi' "@id" FOR XML PATH ('this'), root ('xml');

I was able to figure out the actual type by getting SQL Server to spit out a type-conversion error:

SELECT SQL_VARIANT_PROPERTY((SELECT 'hi' "@id" FOR XML PATH ('this'), root ('xml')), 'BaseType');

Msg 206, Level 16, State 2, Line 1
Operand type clash: nvarchar(max) is incompatible with sql_variant

To fix the warning completely, simply add the TYPE directive to the FOR XML clause:

SET STATISTICS XML ON;
DECLARE @x XML = (SELECT 'hi' "@id" FOR XML PATH ('this'), root ('xml'), TYPE);

The warnings you're seeing most likely come from the sys.sysdepends view.

If you script it out using

EXEC sys.sp_helptext @objname = N'sys.sysdepends'

The definition has a bunch of converts and other nonsense going on.

CREATE VIEW sys.sysdepends AS  
 SELECT  
  id = object_id,  
  depid = referenced_major_id,  
  number = convert(smallint,  
   case when objectproperty(object_id, 'isprocedure') = 1 then 1 else column_id end),  
  depnumber = convert(smallint, referenced_minor_id),  
  status = convert(smallint, is_select_all * 2 + is_updated * 4 + is_selected * 8),  
  deptype = class,  
  depdbid = convert(smallint, 0),  
  depsiteid = convert(smallint, 0),  
  selall = is_select_all,  
  resultobj = is_updated,  
  readobj = is_selected  
 FROM sys.sql_dependencies  
 WHERE class < 2  
 UNION ALL  
 SELECT  -- blobtype dependencies  
  id = object_id, depid = object_id,  
  number = convert(smallint, column_id), depnumber = convert(smallint, type_column_id),  
  status = convert(smallint, 0), deptype = sysconv(tinyint, 1),  
  depdbid = convert(smallint, 0), depsiteid = convert(smallint, 0),  
  selall = sysconv(bit, 0), resultobj = sysconv(bit, 0), readobj = sysconv(bit, 0)  
 FROM sys.fulltext_index_columns  
 WHERE type_column_id IS NOT NULL  

sys.objects, on the other hand, is fairly straightforward.

CREATE VIEW sys.objects AS  
 SELECT name,   
  object_id,  
  principal_id,  
  schema_id,  
  parent_object_id,  
  type,   
  type_desc,   
  create_date,   
  modify_date,  
  is_ms_shipped,  
  is_published,  
  is_schema_published  
 FROM sys.objects$  

The view definition for sys.sysdepends causes the same warnings when queried on its own.

SELECT *
FROM  sys.sysdepends  

In general, if you want to control datatypes and indexes and have some performance tuning ability when referencing system views or tables, your best bet is to dump them into a temp table first.