Question

This MySQL will increment a user’s reputation by 5 when an upvote is submitted.

UPDATE  user_profiles
SET     reputation = reputation +5
WHERE   user_id = $question_author_id;

Now I want to make a distinction:

• if the upvote is for a question, the increment should be 5,
• if the upvote is for an answer, the increment should be 10.

An answer can be identified by the presence of an integer in the field forum_qa_parent_id of table forum_qa.

So I came up with this but it doesn’t work:

UPDATE       user_profiles
IF (SELECT   forum_qa_parent_id 
    FROM     forum_qa 
    WHERE    forum_qa_id = $question_id) IS NOT NULL 
    THEN SET reputation = reputation +10 
    WHERE    user_id = $question_author_id;
ELSE SET     reputation = reputation +5 
WHERE        user_id = $question_author_id;
END IF;

Anyone care to show me how to make this work?

Answer 1

You need to use a CASE statement if you’re doing logical comparisons within a query. http://dev.mysql.com/doc/refman/5.0/en/case-statement.html

UPDATE  user_profiles
SET     reputation = reputation + 
    case when (
        SELECT   forum_qa_parent_id 
        FROM     forum_qa 
        WHERE    forum_qa_id = $question_id) is not null then 10 else 5 end
WHERE   user_id = $question_author_id;

Something along those lines – you might need to touch that one up a bit.