Show only most recent date from joined MySQL table

Question

I have 2 tables, a \"document\" table and a \"content\" table. They look like this (simplified):

document table:
docID
docTitle

content table:
contentID
doc         


        

Answer 1

Use:

SELECT t.docid, 
       t.docTitle, 
       mc.dateAdded, 
       mc.content
  FROM DOCUMENT t
  JOIN (SELECT c.docid,
               c.content,
               MAX(c.dateAdded)
          FROM CONTENT c
      GROUP BY c.docid, c.content) mc ON mc.docid = t.docid 
                                     AND mc.dateadded = t.dateadded

This should be faster than a correlated subquery.

Alternative for when there are no content records for a document:

   SELECT t.docid, 
          t.docTitle, 
          mc.dateAdded, 
          mc.content
     FROM DOCUMENT t
LEFT JOIN (SELECT c.docid,
                  c.content,
                  MAX(c.dateAdded)
             FROM CONTENT c
         GROUP BY c.docid, c.content) mc ON mc.docid = t.docid 
                                     AND mc.dateadded = t.dateadded