SQL Join and show results if join false

Question

I have a table - comments. Users can post if not a member of the site but want to show their details if they are.

So if a user comments who is NOT a member I show their posts but don't link to their profile, because they don't have one.

So, in the following query I want to return the rows even if there is no join:

select wc.comment, wc.comment_by_name, wc.user_id, u.url from comments wc
join users u on wc.wag_uid = u.user_id
where id = '1237' group by wc.comment order by wc.dateadded desc

I want to return:

comment    comment_by_name    user_id    url
-------    ---------------    -------    ----
hello      dan                12         /dan
hey        jane                          /jane
world      jack               10         /jack

But the above does not return the data for jane as she does not have a user_id

Is there a way to return all data even if the join is null?

Answer 1

use LEFT JOIN instead

SELECT  wc.comment, wc.comment_by_name, wc.user_id, u.url 
FROM    comments wc
        LEFT JOIN users u 
           on wc.wag_uid = u.user_id
WHERE id = '1237' 
GROUP BY wc.comment 
ORDER BY wc.dateadded DESC

basically INNER JOIN only select records which a record from one table has atleast one match on the other table while LEFT JOIN select all rows from the left hand side table (in your case, it's comments) whether it has no match on the other table.