# How to format content of a file to fit a SQL in-clause:
# file: username
# with content:
username1
username2
username3
username4
username5
     
# This is how to make it fit the SQL in clause:
sed "s/^/'/;s/$/',/;$ s/,$//" username
     
# output looks like:
'username1',
'username2',
'username3',
'username4',
'username5'
     
# now use output in your SQL statement
select * from users where user_name in
(
<insert output here>
)