php sql using odbc - php

Question

Hi Im making a website in php with a microsoft access database through odbc and i have come across a small problem let me show you my codes first.
<form method ="POST" action="maxtimestamplog.php">
Longitude <input type="text" name="longitude" /><br/>
Latitude
<input type ="text" name = "latitude"/>
<input name="ok" type="submit" value="Submit" />
</form>
<?
$dbc = odbc_connect("X1","",""); // Trying to establish connection
// with database
echo "<br>";
$datetime =date('Y-m-d H:i:s', strtotime('+8 hours'));
echo "The Current date/time is $datetime";
echo "<br><br><br>";
if (!$dbc)
{
exit("Connection failed:".$dbc);
}
$x_origin = $_POST['longitude'];
$y_origin = $_POST['latitude'];
$query = " SELECT m.vehicle_no,
l.longitude,
l.latitude,
l.timestamp
FROM
vehicle_log AS l,
GPS_modem AS m
WHERE
m.modem_ID = l.modem_ID
AND l.timestamp = (
SELECT MAX(timestamp) FROM vehicle_log WHERE modem_ID = l.modem_ID
) order by timestamp desc
"; // SQL Statement
$rs = odbc_exec($dbc,$query);
if (!$rs)
{
exit("Error in SQL. ".$rs);
}
$i=1;
while (odbc_fetch_row($rs))
{
$lng = odbc_result($rs, "longitude");
$lat = odbc_result ($rs, "latitude");
$ts = odbc_result ($rs, "timestamp");
$vno = odbc_result ($rs, "vehicle_no");
$yyyy= substr($ts, 0, 4);
$mm= substr($ts, 5, 2);
$dd= substr($ts, 8,2);
$hr= substr($ts, 11, 2);
$min= substr($ts, 14,2);
$sec= substr($ts,17, 2);
$cyyyy= substr($datetime, 0, 4);
$cmm= substr($datetime, 5, 2);
$cdd= substr($datetime, 8,2);
$chr= substr($datetime, 11, 2);
$cmin= substr($datetime, 14,2);
$csec= substr($datetime,17, 2);
$ctss = $csec
+ ($cmin * 60)
+ ($chr * 60 * 60)
+ ($cdd * 24 * 60 * 60)
+ ($cmm * 30 * 24 * 60 * 60)
+ ($cyyyy * 365 * 24 * 60 * 60);
$tss = $sec
+ (cmin * 60) + ($hr * 60 * 60)
+ ($dd * 24 * 60 * 60)
+ ($mm * 30 * 24 * 60 * 60)
+ ($yyyy * 365 * 24 * 60 * 60);
$tssd = $ctss - $tss;
$x = $lng;
$y = $lat;
$i = $i + 1;
$xd = ($x - $x_origin);
$yd = ($y - $y_origin);
$d = ($xd*$xd) + ($yd*$yd);
$td = sqrt($d);
echo "Car Number $vno is at a distance $td away at timestamp $ts";
echo "</br></br>";
}
odbc_close($dbc);
?>
</HTML>
what I want to be done now is to only display one output not all.
Firstly I want to select only the data where variable $tssd is less than or equal to 10800 then i want to display the smallest $td out of what i selected and it shoud display
echo "Car Number $vno is at a distance $td away at timestamp $ts";
echo "</br></br>";
where $td is the least within $tssd is less than 10800
It should only display one
please try to help me im quite new to php and my sql statement is quite messy as it is i make blunder out of it.

Answer 1

Try to separate the SQL from the PHP.
I believe you're asking how to return only a single row rather than all the rows. To accomplish this, use the "TOP" keyword. For example,
SELECT TOP 1
m.vehicle_no,
l.longitude,
l.latitude,
l.timestamp
For the second part of your question, "where $td is the least within $tssd is less than 10800", we do not know the column names that these relate to. If we pretend they're named TD and TSSD in the vehicle_log table, then your statement might look like this:
SELECT TOP 1 m.vehicle_no,
l.longitude,
l.latitude,
l.timestamp,
l.TD,
l.TSSD
FROM
vehicle_log AS l,
GPS_modem AS m
WHERE
m.modem_ID = l.modem_ID
AND l.timestamp = (
SELECT MAX(timestamp) FROM vehicle_log WHERE modem_ID = l.modem_ID
)
AND l.TD <= 10800
order by l.TD ASC
Lastly, I changed the ORDER BY to accommodate "i want to display the smallest $td".
If this is not what you are looking for, can you provide more information?