Would this work for you?

selec nombre, codigo ;
	from tabla1 ;
	WHERE codigo NOT IN (SELECT codigo FROM tabla2)

it's not a good idea to use one letter meanengless table aliases because i makes code hard to read and could conflict with work area names A-J.

>
>i've a proble i've this datas
>
>tabla1
>
>codigo nombre
>333 pepito
>
>
>tabla2
>
>codigo cta
>
>
>when i write this sentence
>
>selec a.nombre,a.codigo from tabla1 a,tabla2 b where a.codigo<>b.codigo
>
>and the query they have empty , why?? what's the problem.