Question

The following SQL statement:

SELECT f.id, 
       f.front, 
       f.back, 
       h.statusChangedIdCode, 
       h.whenCreated,
       h.historyIdCode 
FROM dpod_site_flashcards AS f 
   JOIN dpod_site_historyItems AS h ON f.id = h.itemId 
WHERE f.id = 216 
  AND historyIdCode = 'statusChanged' 
ORDER BY h.whenCreated

gives me the following output. How do I change it so that it returns only one line which has the most recent statusChangedIdCode?

Answer 1

SELECT f.id, 
       f.front, 
       f.back, 
       h.statusChangedIdCode, 
       h.whenCreated,
       h.historyIdCode 
FROM dpod_site_flashcards AS f 
   JOIN dpod_site_historyItems AS h ON f.id = h.itemId 
WHERE f.id = 216 
  AND h.historyIdCode = 'statusChanged' 
  AND h.whenCreated = (select max(whenCreated)
                       from dpod_site_historyItems h2
                       where h2.itemId = h.itemId
                         and h2.historyIdCode = 'statusChanged')
ORDER BY h.whenCreated

or if you have a modern DBMS supporting windowing functions:

SELECT f.id, 
       f.front, 
       f.back, 
       h.statusChangedIdCode, 
       h.whenCreated,
       h.historyIdCode 
FROM dpod_site_flashcards AS f 
   JOIN (
     select itemid, 
            historyIdCode,
            whenCreated,
            statusChangedIdCode,
            row_number() over (partition by itemid order by whenCreated desc) as rn 
     from dpod_site_historyItems 
     where historyIdCode = 'statusChanged' 
   ) h ON f.id = h.itemId AND h.rn = 1
WHERE f.id = 216 
ORDER BY h.whenCreated

Both cases also work when you select rows for more than one dpod_site_flashcards.id which the LIMIT solution would not do.