MYSQL用例为JOIN参数的一部分

Question

i want to use join when post_type is 1, i'm using case for join but my sql command is not correct. please help me.

mysql:

SELECT SQL_CALC_FOUND_ROWS
                   i. * , 
                   c.title AS category_name, 
                   s.title AS status_title, 
                   i.thumb_image, 
                   CONCAT( u.name, ' ', u.family ) AS author
                FROM contents i
                CASE WHEN post_type = 1 then 
                     JOIN categories c ON c.id = i.category
                end
                JOIN users u ON u.id = i.posted_by
                JOIN status_topics s ON s.id = i.t_status
                WHERE i.id = 2

Answer 1

Why not use if instead of case when?

Syntax:

IF search_condition THEN statement_list
    [ELSEIF search_condition THEN statement_list] ...
    [ELSE statement_list]
END IF

More information here: http://dev.mysql.com/doc/refman/5.0/en/if.html