MySQLi内部联接无法正常工作

Question

I have a query that select shows alongside with it's rating. But it will not work if there isn't any rates. I want it to work even when it finds zero results on the rating table.

My query is

$shows = $DB->query('SELECT
p.id, p.title, p.cover, p.summary, p.genre, p.year, 
ROUND(AVG(pr.rating), 1) AS rating_average
FROM shows p
INNER JOIN shows_ratings pr
ON pr.showid = p.id');

Answer 1

Change inner join with left join.

Explanation: You are trying to join two table on key which doesn't exist in other table, that's why you are not getting any result in inner join. Whereas left join will return rating as empty when key is not present in rating table.

   $shows = $DB->query('SELECT
    p.id, p.title, p.cover, p.summary, p.genre, p.year, 
    ROUND(AVG(pr.rating), 1) AS rating_average
    FROM shows p
    LEFT JOIN shows_ratings pr
    ON pr.showid = p.id');