mysql性能将所有结果输出到phparray或仅在while循环中使用

Question

I have a table which will add about 500,000 rows per year.

I have a query to select rows between value1 and value2, which will output between 100 and 4000 rows. Each row has 5 columns, small data (id fields, and lat long).

I previously had this written using mysql, directly in the code where it was needed, and used a while loop to process and print each row returned by the query.

I am in the process of changing from mysql to mysqli (using procedural if that matters) with prepared statements. During this "changeover", I'm neatening up the code making functions for the queries as they are repeated a lot, so I am including them in a functions.php file.

Because of this, I am now not processing row by row from the mysql result directly in the code, instead I am putting all the rows from the query into an array, then returning from the function, and looping through one by one in the code where it is needed.

Bit of code for reference:

function...
...
        mysqli_stmt_bind_result($stmt,
        $id,
        $heading,
        $journey,
        $lat,
        $lon);

$map_array = array();
$n=0;
           while (mysqli_stmt_fetch($stmt)) {


               //output to array
               $map_array[$n]['id'] = $id;
               $map_array[$n]['heading'] = $heading;
               $map_array[$n]['journey'] = $journey;
               $map_array[$n]['lat'] = $lat;
               $map_array[$n]['lon'] = $lon;
$n=$n+1;
}
return $map_array;
}

And Then I would have to loop through the array and process it in the code.

In comparison to my old way:

$lasthead ='0';
while ($row=mysql_fetch_array($result)){
$lat = $row['lat'];
$lon = $row['lon'];
$id = $row['id'];
$heading = $row['heading'];
$journey = $row['journey'];

$doprint='1';
if ($journey =='2' && $heading !==''){
    $maxvar = max($heading, $lasthead);
    $minvar = min($heading, $lasthead);
    $headdiff = $maxvar - $minvar;
    if ($headdiff < 1.5)  { $doprint = '0'; }  
}
if ($doprint =='1'){ print "new google.maps.LatLng($lat, $lon),\n";}

$doprint='1';
$lasthead = $heading;
$heading ='';
}

Question. Is loading all results into an array, then processing the array a bad idea performance wise? vs a while loop processing the mysql result by row.

Thanks

Answer 1

You don't gain anything by going through the records twice. Do all of your work in the mysql fetch loop.

The only times you wouldn't want to do that is if

1. What you are doing in the loop is expensive (in terms of time) and you want to close the statement handle.

2. You have to walk through the data multiple times.