Question

I have menu and action tables which share links between by one-to-one table:

menu: id, name
action: id, name
MenAct: menu_id, action_id

Not all menu.id in MenAct.menu_id set (in other words some menu have no associated action)…

I can’t write select, which give pairs of menu.name, action.name when:

menu.id = MenAct.menu_id AND action.id = MenAct.action_id

and menu.name, NULL otherwise…

This require nested request or other SQL techniques but I am very noob to Oracle SQL.

Answer 1

Sounds like you want a LEFT JOIN not an INNER JOIN:

select m.name, a.name
from menu m
left join menuact ma
    on m.id = ma.menu_id
left join action a
    on ma.action_id = a.id

A LEFT JOIN will return all rows from the menu table regardless of whether it has a matching row in the other tables. If it does not exist then you will have a null value in action.

If you need help learning JOIN syntax, here is a great visual explanation of joins