I have the following query
SELECT * FROM table
WHERE tester <> 'username';
where clause will return all rows where
tester does not match
username AND where
tester is not null.
If you want to include NULLs, try:
where tester <> 'username' or tester is null
If you are looking for strings that do not contain the word "username" as a substring, then
like can be used:
where tester not like '%username%'