results = c.execute(select).fetchall()

stroka = ''
for line in results:
    stroka = stroka + str(line) + 'n'

self.ui.textEdit.setText(stroka)

text = 'n'.join([str(line) for line in results])

text = 'n'.join(map(str, results))

sqlite> select * from tab;
s
----------
111
222
333

sqlite> select group_concat(s,'') from tab;
group_concat(s,'')
------------------
111222333

sqlite> select group_concat(s,'n') from tab;
group_concat(s,'n')
--------------------
111n222n333