declare @c int = 20000;
declare @sql nvarchar(max) = N'declare @n int; select @n = Number from master.dbo.spt_values where Number in (%list%)';
declare @list nvarchar(max);

select
 @list = stuff(t.x.value('.', 'nvarchar(max)'), 1, 2, '')
from
 (
  select top (@c)
   ', ' + cast(row_number() over (order by 1/0) as nvarchar(10))
  from
   master.dbo.spt_values a cross join
   master.dbo.spt_values b
  order by
   newid()
  for xml path(''), type
 ) t(x);

set @sql = replace(@sql, '%list%', @list);

--set statistics xml on;

print '---------------------------';
print 'in()';
print '---------------------------';
set statistics io, time on;
exec sys.sp_executesql @sql;
set statistics io, time off;


set @sql = N'declare @n int;

select
 @n = a.Number
from
 master.dbo.spt_values a
where
 exists(select 1 from string_split(@list, '','') where cast(Value as int) = a.Number);'

print '---------------------------';
print 'string_split()';
print '---------------------------';
set statistics io, time on;
exec sys.sp_executesql @sql, N'@list nvarchar(max)', @list;
set statistics io, time off;

--set statistics xml off;

---------------------------
in()
---------------------------
SQL Server parse and compile time: 
   CPU time = 2313 ms, elapsed time = 2319 ms.
Table 'Workfile'. Scan count 0, logical reads 0, physical reads 0, page server reads 0, read-ahead reads 0, page server read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob page server reads 0, lob read-ahead reads 0, lob page server read-ahead reads 0.
Table 'Worktable'. Scan count 0, logical reads 0, physical reads 0, page server reads 0, read-ahead reads 0, page server read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob page server reads 0, lob read-ahead reads 0, lob page server read-ahead reads 0.
Table 'spt_values'. Scan count 1, logical reads 13, physical reads 0, page server reads 0, read-ahead reads 0, page server read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob page server reads 0, lob read-ahead reads 0, lob page server read-ahead reads 0.

 SQL Server Execution Times:
   CPU time = 0 ms,  elapsed time = 2 ms.

 SQL Server Execution Times:
   CPU time = 2313 ms,  elapsed time = 2322 ms.
---------------------------
string_split()
---------------------------
SQL Server parse and compile time: 
   CPU time = 0 ms, elapsed time = 0 ms.
Table 'spt_values'. Scan count 20000, logical reads 40000, physical reads 0, page server reads 0, read-ahead reads 0, page server read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob page server reads 0, lob read-ahead reads 0, lob page server read-ahead reads 0.
Table 'Worktable'. Scan count 0, logical reads 0, physical reads 0, page server reads 0, read-ahead reads 0, page server read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob page server reads 0, lob read-ahead reads 0, lob page server read-ahead reads 0.

 SQL Server Execution Times:
   CPU time = 46 ms,  elapsed time = 46 ms.

 SQL Server Execution Times:
   CPU time = 46 ms,  elapsed time = 46 ms.

Completion time: 2020-12-07T18:02:31.6391806+03:00