I have a valid MySQL Query that selects the latest occupancy percentage of a table from each community entered in my DB, but it seems to be scanning the entire DB of entries as the lookup time takes roughly 3-4 seconds.
With the details provided in the query below, can someone provide me with a faster/better way to lookup the latest timestamp field for each community? - I need the query to select every community entered, with the latest timestamp, but the limit for each community selected should be 1 (meaning community named "Test Community" will have possibly hundreds of submissions but I need the latest entered Timestamp selected, along with the same selection for every community entered in the table)
SELECT t1.reportID, t1.communityID, t1.region, t1.percentOccupied,
t1.TIMESTAMP, Communities.fullName
FROM NightlyReports t1
INNER JOIN Communities On t1.communityID = Communities.communityID
WHERE t1.TIMESTAMP = ( SELECT MAX( TIMESTAMP ) FROM NightlyReports WHERE
t1.communityID = NightlyReports.communityID )
AND t1.region = 'GA' ORDER BY percentOccupied DESC
In my experience, correlated subqueries often have rather poor performance; try this instead:
SELECT t1.reportID, t1.communityID, t1.region, t1.percentOccupied
, t1.TIMESTAMP, Communities.fullName
FROM NightlyReports AS t1
INNER JOIN Communities ON t1.communityID = Communities.communityID
INNER JOIN (
SELECT communityID, MAX( TIMESTAMP ) AS lastTimestamp
FROM NightlyReports
WHERE region = 'GA'
GROUP BY communityID
) AS lastReports ON t1.communityID = lastReports.communityID
AND t1.TIMESTAMP = lastReports.lastTimestamp
WHERE t1.region = 'GA'
ORDER BY percentOccupied DESC