Question

I have three tables.
First table is Activities and second is Members and last is Message.
Activities has a foreign key named Members_ID and primary key is Activity_ID.
Members’ primary key is Members_ID.
Message recorded Activity_ID and Members_ID.
I wanna search about Activities NATURAL JOIN Members and I need a new column count for
Message’s message_ID where the Activity_ID is the same.

NATURAL JOIN:

SELECT*
    FROM Activities 
        NATURAL JOIN Members 
    WHERE Activities.Members_ID = Members.Members_ID;

COUNT(message_ID):

SELECT COUNT(message_ID) 
    FROM Message 
    WHERE Activity_ID = 123;

Question is:
How to search the above two things together?
I’d like have a table have Activities NATURAL JOIN Members with same Activities.Members_ID
and a virtual column which is COUNT(message_ID) from table Message.

Answer 1

Perhaps you wish to use a correlated subquery, like this:

SELECT *, (SELECT COUNT(message_ID) FROM Message WHERE Activity_ID = a.Activity_ID AND Members_ID = m.Members_ID) AS Message_Count
    FROM Activities AS a
        NATURAL JOIN Members AS m
    WHERE a.Members_ID = m.Members_ID;

But, I would avoid the natural join syntax:

SELECT *, (SELECT COUNT(message_ID) FROM Message WHERE Activity_ID = a.Activity_ID AND Members_ID = m.Members_ID) AS Message_Count
    FROM Activities AS a
        JOIN Members AS m on a.Members_ID = m.Members_ID;