Question

I cannot seem to find the error in my MySQL query. It states that I have not unique table alias for table usuarios_grupos

However, my table usuarios_grupos only appears once!

My query is the following:

SELECT DISTINCT usuarios.id_usuario
FROM usuarios
WHERE usuarios.id_usuario
NOT IN 
(SELECT DISTINCT id_usuario FROM usuarios_grupos, grupos
WHERE usuarios_grupos.id_grupo = grupos.id_grupo)

Any idea why this is happening?

Answer 1

Your table usuarios_grupos appears once but id_usuario might be in two tables so you have to be specific and try use join instead and there are no need for Distict like this:

SELECT usuarios.id_usuario
FROM usuarios
WHERE usuarios.id_usuario
NOT IN 
(
   SELECT ug.id_usuario 
   FROM usuarios_grupos ug inner join grupos g 
   on ug.id_grupo = g.id_grupo
)