I'm completely stumped: checking two tables against eachother in MySQL query

Question

I feel like I'm writing a word problem, but it's really puzzling me and I really hope someone here can solve it:

I want to select one row from table A. Table A includes the attributes Name and Number. But before I finish the query, I want to check it against table B. Table B includes Name, Number, and the Username of the user. Based on the users' input, it inserts rows into table B that include their Username along with a Name and Number. Now in my query where I select a row from table A, I want to make sure that there are no rows in table B with matching Name and Number for that particular User.

I have tried WHERE (A.Name = B.Name AND A.Number = B.Number AND B.Username != '$username') but I think I was way off base with that. Any help would be... amazing.

Answer 1

SELECT
   A.id
FROM
   A
   LEFT OUTER JOIN B ON
      (A.Name = B.Name AND A.Number = B.Number)
WHERE
   B.Name IS NULL
   AND B.Number IS NULL
   AND B.Username = ?

Answer 2

  IF NOT EXISTS  ( SELECT 1 
       FROM tableA a
       INNER JOIN tableB b
       ON a.name = b.name
       AND a.number= b.number
       AND b.UserName = 'user' and b.name = 'name'and b.number = 'number')
  SELECT *
  FROM tableA x
  WHERE x.name = 'name'and x.number = 'number'

Answer 3

select a.id
from a
where
a.name=:name
and
not exists(select 1 from b where b.id=a.id and b.name=a.name)