How can I select the set of rows where each item has the greatest timestamp?

Question

Using Sqlite, I\'d like to fetch the collection of rows each with the greatest timestamp. The table contains the properties of items, which are key-value pairs and timestamp

Answer 1

In SQLite 3.7.11 or later, you can simply use MAX() to select one row from a group:

SELECT key, value, MAX(timestamp)
FROM Properties
WHERE thing = 'watermelon'
GROUP BY key;

Answer 2

Use HAVING for simple and readable solution:

SQLFiddleDemo

SELECT *
FROM Properties
WHERE thing = "watermelon"
GROUP BY thing, key
HAVING timestamp = MAX(timestamp)

Answer 3

Tweaking the query found here, I've come up with the following:

SELECT a.* 
FROM Properties AS a 
INNER JOIN (
  SELECT key, MAX(timestamp) AS max_timestamp 
  FROM Properties 
  WHERE thing='watermelon' 
  GROUP BY key) b 
ON a.key = b.key AND a.timestamp = b.max_timestamp 
WHERE thing='watermelon';

Seems to work, though I'd be interested in comments the pros/cons of this query.