Question

I have 3 tables :

• wp_users – stores main information about all users,
• wp_usermeta – stores additional information about users(first/last name/etc),
• wp_friends – stores information about friends from third party services related to a specific user from wp_users

If you are not familiar with WordPress, you can see the structure of both tables at http://codex.wordpress.org/images/9/9e/WP3.0-ERD.png

The structure of my custom table wp_friends is as follows:

CREATE TABLE wp_friends (
    id bigint(20) unsigned NOT NULL auto_increment,
    uid bigint(20) unsigned NOT NULL default '0',
    fr_id VARCHAR (60) NOT NULL default '',
    service VARCHAR (20) NOT NULL default '',
    name VARCHAR (80) NOT NULL default '',
    photo VARCHAR (255) NOT NULL default '',
    PRIMARY KEY (id),
    KEY uid (uid),
    KEY fr_id (fr_id),
    KEY service (service)
)`

The uid column is corresponds to the ID column in the wp_users table – this is how I determine which record corresponds to which user.

What I’m trying to do is to create a query that will look in all of the three tables for a match against a keyword. Here is what I’ve come with so far(the first part was generated by a search function of WordPress):

SELECT 
    wp_users.ID,wp_users.display_name,wp_users.user_login,
    wp_users.user_email,fr.fr_id,fr.name,fr.photo,fr.service
    FROM wp_users

    INNER JOIN wp_usermeta ON (wp_users.ID = wp_usermeta.user_id)

    LEFT JOIN wp_socialaccess_friends AS fr ON fr.uid = 2

    WHERE 
    (
        (user_login LIKE '%nik%' OR user_nicename LIKE '%nik%')
        AND 
        (wp_usermeta.meta_key = 'wp_user_level' AND CAST(wp_usermeta.meta_value AS CHAR) != '0')
    )
    OR ( fr.uid = 2 AND (fr.fr_id LIKE '%nik%' OR fr.name LIKE '%nik%'))

    GROUP BY wp_users.ID,fr.fr_id ORDER BY user_login ASC

In the above query, the keyword is “nik”(which also matches a user_login column). The fr.uid part is needed so the returned results are only for the current user. The query fails in the following ways:

• It returns all rows from the wp_friends table(because the user_login column is matched as well), that have wp_friends.uid = 2
• It returns rows that have wp_friends.uid = 2 but matched with users where wp_users.ID != 2

Is it possible to create a single query, that would return the selected columns, but will also prevent duplicates?

Answer 1

What about joining on a sub-select like:

SELECT 
    wp_users.ID,wp_users.display_name,wp_users.user_login,
    wp_users.user_email
    FROM wp_users

    INNER JOIN wp_usermeta ON (wp_users.ID = wp_usermeta.user_id)
    left join(
      select fr_id, uid,name,photo,service from wp_socialaccess_friends where
            uid = 2 and
            (fr_id LIKE '%nik%' OR name LIKE '%nik%')
        ) AS fr ON wp_users.ID = fr.uid 

    WHERE 
    (
        (user_login LIKE '%nik%' OR user_nicename LIKE '%nik%')
        AND 
        (wp_usermeta.meta_key = 'wp_user_level' AND CAST(wp_usermeta.meta_value AS CHAR) != '0')
    )

    GROUP BY wp_users.ID,fr.fr_id ORDER BY user_login ASC