Question

I have two tables as user_shows, and comments. They both have a key in common as id.

I want to have a column in user_shows, which will store the number of comments in the comments table when user_shows.id = comments.id. I tried, and came up with something like:

ALTER TABLE user_shows 
ADD num_comments INT(4) AS (SELECT id 
                              FROM comments, 
                                   user_shows 
                             WHERE comments.id = user_shows.id)

…but this didn’t work.

Answer 1

you have to write two separate queries like this:-

ALTER TABLE user_shows 
ADD num_comments INT(4);

UPDATE user_shows SET num_comments = (SELECT count(id) FROM comments WHERE comments.id = user_shows.id);