How to emulate full outer join in this query?

Question

So apparently mySQL doesn\'t support full outer join, but it\'s really what I need. I\'ve seen a bunch of blog posts and articles about emulating it with unions, but that remove

Answer 1

You basically do a Union of LEFT and RIGHT JOIN.

You actually have interesting wrinkle in that you also want to limit the rows to 3. To solve that you need to

• Limit both The "left" and "right" selects by 3
• Then use the result of the UNION in a inline view
• then Limit the union by 3 again

UPDATE Sadly, unless I'm mistaken you can't do this directly in a UNION so you need to add another layer of inline views prior to the UNION

The LIMITS inside the UNION will offer some performance benefit and then the limit after will give you the correct results.

SELECT title, 
   teaser, 
   nid, 
   DATE, 
   image, 
   image_tid 
FROM   (SELECT title, 
               teaser, 
               nid, 
               DATE, 
               image, 
               image_tid,
               created 
        FROM   (SELECT DISTINCT n.title, 
                                nr.teaser, 
                                n.nid, 
                                Date_format(From_unixtime(n.created), 
                                '%M %e, %Y') AS 
                                DATE, 
                                f.filepath 
                                AS 
                                image, 
                                tn_img.tid 
                                AS 
                                image_tid 
                                       , 
                                n.created 
                FROM   node n 
                       JOIN node_revisions nr 
                         ON n.nid = nr.nid 
                       LEFT JOIN content_field_related_images cfri 
                         ON ( n.nid = cfri.nid 
                              AND cfri.delta = 0 ) 
                       LEFT JOIN content_field_att_file cfaf 
                         ON cfri.field_related_images_nid = cfaf.nid 
                       LEFT JOIN files f 
                         ON cfaf.field_att_file_fid = f.fid 
                       JOIN term_node tn2 
                         ON n.nid = tn2.nid 
                       LEFT OUTER JOIN term_node tn_img 
                         ON cfri.field_related_images_nid = tn_img.nid 
                WHERE  n.status = 1 
                       AND n.TYPE = 'article' 
                       AND nr.body LIKE '%kimberly-clark%' 
                       AND tn2.tid = 143 
                ORDER  BY n.created DESC 
                LIMIT  3) tleft 
        UNION 
        SELECT title, 
               teaser, 
               nid, 
               DATE, 
               image, 
               image_tid,
               created  
        FROM   (SELECT DISTINCT n.title, 
                                nr.teaser, 
                                n.nid, 
                                Date_format(From_unixtime(n.created), 
                                '%M %e, %Y') AS 
                                DATE, 
                                f.filepath 
                                AS 
                                image, 
                                tn_img.tid 
                                AS 
                                image_tid 
                                       , 
                                n.created 
                FROM   node n 
                       JOIN node_revisions nr 
                         ON n.nid = nr.nid 
                       LEFT JOIN content_field_related_images cfri 
                         ON ( n.nid = cfri.nid 
                              AND cfri.delta = 0 ) 
                       LEFT JOIN content_field_att_file cfaf 
                         ON cfri.field_related_images_nid = cfaf.nid 
                       LEFT JOIN files f 
                         ON cfaf.field_att_file_fid = f.fid 
                       JOIN term_node tn2 
                         ON n.nid = tn2.nid 
                       RIGHT OUTER JOIN term_node tn_img 
                         ON cfri.field_related_images_nid = tn_img.nid 
                WHERE  n.status = 1 
                       AND n.TYPE = 'article' 
                       AND nr.body LIKE '%kimberly-clark%' 
                       AND tn2.tid = 143 
                ORDER  BY n.created DESC 
                LIMIT  3) tright) t 
ORDER  BY created DESC 
LIMIT  3 

UPDATE Using spencer7593 and ypercube suggestions here's an alternative approach using two UNION ALL statements and no inline views.

SELECT DISTINCT n.created, 
                n.title, 
                nr.teaser, 
                n.nid, 
                Date_format(From_unixtime(n.created), '%M %e, %Y') AS DATE, 
                f.filepath                                         AS image, 
                tn_img.tid                                         AS image_tid 
FROM   node n 
       JOIN node_revisions nr 
         ON n.nid = nr.nid 
       LEFT JOIN content_field_related_images cfri 
         ON ( n.nid = cfri.nid 
              AND cfri.delta = 0 ) 
       LEFT JOIN content_field_att_file cfaf 
         ON cfri.field_related_images_nid = cfaf.nid 
       LEFT JOIN files f 
         ON cfaf.field_att_file_fid = f.fid 
       JOIN term_node tn2 
         ON n.nid = tn2.nid 
       LEFT OUTER JOIN term_node tn_img 
         ON cfri.field_related_images_nid = tn_img.nid 
WHERE  n.status = 1 
       AND n.TYPE = 'article' 
       AND nr.body LIKE '%kimberly-clark%' 
       AND tn2.tid = 143 

UNION ALL 
SELECT DISTINCT n.created, 
                n.title, 
                nr.teaser, 
                n.nid, 
                Date_format(From_unixtime(n.created), '%M %e, %Y') AS DATE, 
                f.filepath                                         AS image, 
                tn_img.tid                                         AS image_tid 
FROM   node n 
       JOIN node_revisions nr 
         ON n.nid = nr.nid 
       LEFT JOIN content_field_related_images cfri 
         ON ( n.nid = cfri.nid 
              AND cfri.delta = 0 ) 
       LEFT JOIN content_field_att_file cfaf 
         ON cfri.field_related_images_nid = cfaf.nid 
       LEFT JOIN files f 
         ON cfaf.field_att_file_fid = f.fid 
       JOIN term_node tn2 
         ON n.nid = tn2.nid 
       RIGHT JOIN term_node tn_img 
         ON cfri.field_related_images_nid = tn_img.nid 
WHERE  n.status = 1 
       AND n.TYPE = 'article' 
       AND nr.body LIKE '%kimberly-clark%' 
       AND tn2.tid = 143 
       AND cfri.field_related_images_nid IS NULL 
ORDER  BY 1 DESC 
LIMIT 
3