Combine column from multiple rows into one row in SQLITE

This is relatively trivial to do with a correlated subquery. You can't use the COALESCE method highlighted in the blog post you mention unless you extract that to a user-defined function (or unless you only want to return one row at a time). Here is how I typically do this:

DECLARE @x TABLE 
(
  id INT, 
  row_num INT, 
  customer_code VARCHAR(32), 
  comments VARCHAR(32)
);

INSERT @x SELECT 1,1,'Dilbert','Hard'
UNION ALL SELECT 1,2,'Dilbert','Worker'
UNION ALL SELECT 2,1,'Wally','Lazy';

SELECT id, customer_code, comments = STUFF((SELECT ' ' + comments 
    FROM @x AS x2 WHERE id = x.id
     ORDER BY row_num
     FOR XML PATH('')), 1, 1, '')
FROM @x AS x
GROUP BY id, customer_code
ORDER BY id;

If you have a case where the data in comments could contain unsafe-for-XML characters (>, <, &), you should change this:

     FOR XML PATH('')), 1, 1, '')

To this more elaborate approach:

     FOR XML PATH(''), TYPE).value(N'(./text())[1]', N'varchar(max)'), 1, 1, '')

(Be sure to use the right destination data type, varchar or nvarchar, and the right length, and prefix all string literals with N if using nvarchar.)

I think this will give you desired resultset :

select id,grp,itdesc,
MAX(CASE WHEN su=1 THEN DEN END) AS DEN,
MAX(CASE WHEN su=1 THEN NUM END) AS NUM,
MAX(CASE WHEN su=1 THEN SU END) AS SU ,  -- or just  "1 AS SU" 
MAX(CASE WHEN cs=1 THEN NUM END) AS CS,
MAX(CASE 
   WHEN sw=1 THEN NUM  
   WHEN sw=0 THEN 0 
   END) AS SW
FROM tab
GROUP BY 
id,grp,itdesc