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

Could you not just do a simple join, and order by date added, and grab only the first record?

SELECT docTable.docId, docTable.docTitle from docTable
INNER JOIN content ON content.docID = docTable.contentID
WHERE docTable.docId = <some id>
ORDER BY content.dateAdded DESC

Answer 2

This is a 2 query solution:

First query:

select docID, max(dateadded) from [TblContent] group by docID

Second query:

select [TblDocument].* from [TblDocument]  
inner join [TblDocument] on [TblDocument].[Docid]=[FirstQuery].[DocID]

Answer 3

This can be done with a subquery:

SELECT d.docID, docTitle, c.dateAdded, c.content
FROM document d LEFT JOIN content c ON c.docID = d.docID
WHERE dateAdded IS NULL
    OR dateAdded = (
        SELECT MAX(dateAdded)
        FROM content c2
        WHERE c2.docID = d.docID
    )

This is known as a "groupwise maximum" query

Edit: Made the query return all document rows, with NULLs if there is no related content.

Answer 4

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

Answer 5

try this:

select d.id, d.docTitle, MAX(c.dateAdd)
from document_table d
left join content_table c
on d.id = c.docId
group by d.id

Here is the thinking behind it: suppose document table has record A related to content(1, 2, 3, 4) and B related to (5, 6, 7, 8)

document        content

A               1
            2
                    3
            4

B               5
            6
            7
            8

a inner join with max(dateadded) will give you

document        content     max(dateadded)

A               1           1-1-2009...

A               2           1-1-2009...

A               3           1-1-2009...

A               4           1-1-2009...

B               5           2-1-2009...

B               6           2-1-2009...

B               7           2-1-2009...

B               8           2-1-2009...

after group by document id you will get

document    content     max(dateadded)

A           1           1-1-2009...

B           5           2-1-2009...

note: content id does not necessary match the id of the max dateadded