Sql-server – Type conversion in expression try_cast may affect cardinality estimate in query plan choice

The result of the query seems to be correct and the server executes it quickly.

But the root node of the execution plan has a warning:

Type conversion in expression (CONVERT_IMPLICIT(nvarchar(128),[o].[name],0)) may affect "CardinalityEstimate" in query plan choice

What does that mean in this context? Is such a complex filter confusing the optimizer? Is it something I should be worried about?

The warning is informational. If your query performed slowly, or you noticed that cardinality estimates were incorrect, the warning would give you information about where to look for a possible cause.

The warning is triggered by the implicit conversion used for the collation change. If using the collation is the easiest way to get correct results, feel free to leave it as it is. Alternatively, if you explain more about why it is needed, someone will advise you.

As an aside, the REPLACE could be replaced with:

REPLICATE(N'[0-9A-F]', 8);

(This answer is a summary of the comments to the question.)

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.