Convert column values into string - sql

Question

I'm trying to write e proc which will convert column values into a string separated with a character: ',' for example.
it stucks on this line exec #maxcount = sp_executesql #temp and returns the value of #maxxount any suggestions how could I set a value of dynamic query execution so that it continued processing all the function an executed the correct answer.
ALTER procedure [dbo].[usp_stringConvert](
#table_name varchar(101),
#column_name varchar(100),
#separator varchar(20)
)
as
declare #maxcount int, #temp nvarchar(1000)
declare #count int
declare #result varchar(1000)
set #result =''
set #count =1
set #temp= Concat('select count(', #column_Name ,') from ', #table_name)
exec #maxcount = sp_executesql #temp
while (#count<#maxcount)
begin
if #count!=1
set #result+=#separator
set #temp=Concat('select ' , #column_name ,' from ' , #table_name , 'where #count = row_number() over(order by (select (100)))')
exec #temp = sp_executesql #temp
set #result =CONCAT(#result, #temp)
set #count+=1;
end
select #result;

Answer 1

Using regular SQL in SQL Server, you can concatenate strings using:
select stuff( (select concat(separator, column_name)
from table_name
for xml path ('', type)
).value('.', nvarchar(max)
), 1, len(separator), ''
)
You should be able to turn this into dynamic SQL using:
declare #sql nvarchar(max);
declare #result nvarchar(max);
set #sql = N'
select #result = stuff( (select concat(#separator + [column_name]
from [table_name]
for xml path ('''', type)
).value(''.'', nvarchar(max)
), 1, len(#separator), ''
)
';
set #sql = replace(#sql, '[table_name]', quotename(#table_name));
set #sql = replace(#sql, '[column_name]', quotename(#column_name));
exec sp_executesql #sql,
N'#result nvarchar(max) output',
#result=#result output;
select #result;