Question

How can I use a single query for inserting table when a column value is not found.
eg/ i want to insert new user only when this username not found

what i doing now is issue 1 query to check for existing,
then another query if no existing found. total 2 query

 INSERT INTO friends (memberID) SELECT 1 WHERE NOT EXISTS (SELECT memberID FROM friends WHERE memberID =  1)

Answer 1

You just need to add FROM DUAL

INSERT INTO friends 
            (memberid) 
SELECT 1 
FROM   dual 
WHERE  NOT EXISTS (SELECT memberid 
                   FROM   friends 
                   WHERE  memberid = 1)

sql fiddle