Question

What I’m trying to do is grab entries from an updates table in a mysql database using php. Each entry has a timestamp attached to it. First, I grab 10 distinct dates from the timestamp, create a new array using those 10 unique dates (I do this because the fetchAll put the dates into a multidimensional array), then do another database call grabbing all entries that has those dates. Which can return more than 10 entries. I want it to have 10 distinct dates, not 10 distinct timestamps.

For example, if 2012-03-25 showed up in the first call from distinct dates, it can find:

2012-03-25 00:58:53
2012-03-25 00:58:02
2012-03-25 00:57:20
2012-03-25 00:56:35
2012-03-25 00:55:58
2012-03-25 00:53:20
2012-03-25 00:52:32
2012-03-25 00:51:45

Since the timestamps are different.

Here is the current code I am using, which works.

$test = $dbh->getArray("SELECT DISTINCT DATE_FORMAT(added, '%Y-%m-%d') AS added FROM db_updates ORDER BY added DESC LIMIT 0,10");

foreach ($test as $entry) {
  list($date) = $entry;
  $output[] = '\''.$date.'\'';
}  

$test2 = $dbh->getArray("SELECT * FROM db_updates WHERE DATE_FORMAT(added, '%Y-%m-%d') IN (".implode(',', $output).") ORDER BY added DESC");

print_r($test2);

This returned 33 results.

Just in case anyone ask, I am using PDO and not the mysql function in php. That code is here:

public function getArray($query) {
  $result = $this->db->query("$query");
  return $result->fetchAll(PDO::FETCH_NUM);
}

This all works 100%, and it does what I want it to do. However, my question is if there is a way to do all this with just a single mysql call, so I don’t have to call twice with a loop in the middle.

I tried to figure it out myself by searching google, and trial and error using joins and such to no avail.

Answer 1

It should work with an INNER JOIN, and you can just use DATE(added) instead of DATE_FORMAT() to strip off the time portion of the DATETIME values:

SELECT * 
FROM
  db_updates
  INNER JOIN (
    /* Subquery returns most recent 10 dates */
    SELECT DISTINCT DATE(added) AS added FROM db_updates ORDER BY added DESC LIMIT 0,10
  /* JOIN between dates */
  ) datelist ON DATE(db_updates.added) = datelist.added
ORDER BY db_updates.added DESC