Double query in 1 query

Question

I have 2 tables one of users and another of subscribers, I have an Internet that sends to the table of subscribers the email of the user who registered and the name of the channel

1st users

id | usuario  | meucanal 
1  | [email protected]  | portados fundos 
2  | [email protected]  | parafernalha
3  | [email protected]  | Ei nerd
4  | [email protected]  | Canal Nostalgia

2nd entries

id | usuario | se_inscreveu_no_canal
1  | [email protected]   | Ei nerd
2  | [email protected]   | parafernalha

Summarizing what I need is to make a SELECT list only the channels that the user has not yet registered in the case of the example the [email protected] needs to be displayed only the Nostalgia Channel

$sql = "SELECT * FROM usuarios WHERE canal NOT EXIST IN(SELECT * FROM inscricoes WHERE o_usuario NOT IN se_inscreveu_no_canal) ORDER BY RAND();

I’m not a professional in the area, I just program as a hobby to make things simpler and this type of consultation is more advanced if you can help me in a way to solution since I thank you.

Follows a bit of structure for better understanding(well summarized)

php.

enter your email and channel name

INSERT INTO usuarios (usuario, canal) VALUES ('$_POST[email]',$_POST[canal]')"; READY REGISTER

listarcanais.php ( the user in this part is already logged in $user=Session[email]) SELECT * FROM usuarios ORDER BY canal LIMIT 1"; echo " CLICK HERE FOR YOURSELF ";

subscribe.php ( the user in this part is already logged in $user=Session[email]) $canal= $GET[canal]; INSERT INTO entries (user, channel) VALUES ('$user,$channel')"; //redirect to listarcanais.php PRONTO JA APPEARS IN THE COMIC BOOK THAT THE USER HAS ALREADY ENTERED IN THAT CHANNEL

listarcanais.php <<< as in my head think the system should read

SELECT CHANNEL FROM (table users) WHERE the (user=$user) DID NOT register ( in the table entries)

roughly: 1° a select that takes the (email/$user) and compares the USERS and SUBSCRIPTIONS tables in order to delete the other email that is not the $user one

done this 2° a select that lists all channels of the USUARIOS table and compares with all channels of the INSCRIPTIONS table. Those who are not equal will be listed

Answer 1

SELECT
    distinct(canal)
FROM
    usuarios
WHERE
    email <> '$email'
    AND
    canal NOT IN (
        SELECT canal FROM inscricoes WHERE email = '$email'

   )

Answer 2

There are only these two tables, there is no channel table? How is all existing channels recorded?

Having three tables: Usuarios, Canais and Inscricoes, where Inscricoes is many-to-many relationship between Usuarios and Canais, so just bring the Canais that do not exist in Inscricoes for Usuarios.

select u.nome as usuario, c.nome as canal
from usuarios u, canais c
where not exists (select 1 from inscricoes i where i.cod_canal =c.cod_canal and i.cod_usuario = u.cod_usuario);