randomly choose one data from blocks of query - php

Question

I have 100000 records in a table. I need to make a query that reads 10 records and after that 10 more records continuously until the end of the table. For each of the 10 rows groups, I need to pick one random row. Is it possible to accomplish that using a MySQL query? I need some idea to do this. Can anybody help me?
I have tried to do a php loop but it doesn't work.
<?php
include_once ("connection.php");
$data = mysql_query("SELECT * FROM trying");
$result = array();
while ($data2 = mysql_fetch_array($data))
{
array_push($result, array('no'=> $data2['no'],
'source'=> $data2['source'],
'destination'=> $data2['destination']));
}
$e=0;
for ($a = 0; $a <= 49;)
{
for ($i = 0; $i <= 9; $i++,$a++) {
$rand = array();
$rand[$i] = $result[$a];
}
echo json_encode($rand[1]);
}
?>

Answer 1

Insted of this:
for ($a = 0; $a <= 49;)
{
for ($i = 0; $i <= 9; $i++,$a++) {
$rand = array();
$rand[$i] = $result[$a];
}
echo json_encode($rand[1]);
}
you can use this:
$rand = array();
$step = 10;
for ($min = 0; $min <= 49; $min = $min + $step)
{
$max = $min + $step;
$rand[] = $result[rand($min,$max)];
}
echo json_encode($rand);

Answer 2

Since you're echoing a json encoded array, I'm assuming you're calling this php file through an AJAX request, and you want subsequent requests for each 10 rows.
If this is the case, a solution to your problem could be this:
Define limit and offset as vars in your javascript
Pass limit and offset with the AJAX request
If the result of the AJAX request isn't empty, increment offset by limit (offset = offset + limit) to use in the next request
Receive limit and offset in the PHP file (use $_GET or $_POST, depends on the type of request)
Include limit and offset in the MySQL query ("SELECT * FROM trying LIMIT $offset, $limit")
Calculate a random number from 0 to 9 (rand(0, 9))
Fetch the nth (rand) row from the MySQL result (see solution below)
Your PHP file should look like this:
include_once ("connection.php");
$limit = mysql_real_escape_string($_GET['limit']); // If post use $_POST
$offset = mysql_real_escape_string($_GET['offset']); // If post use $_POST
$data = mysql_query("SELECT * FROM trying LIMIT $offset, $limit");
$rand = rand(0, 9);
$count = 0;
while($row= mysql_fetch_array($data)) {
if($rand == $count++) {
echo json_encode($row);
break;
}
}

Answer 3

Put the SQL statement in a loop and use the counter as a variable in the Limit:
$count = mysql_query("SELECT * FROM trying");
$total = round(mysql_num_rows($count) / 10);
for ($i=0;$i<$total;$i++) {
$data = mysql_query("SELECT * FROM trying LIMIT ".($i * 10).", 10");
$result = array();
while ($data2 = mysql_fetch_array($data))
{
array_push($result, array('no'=> $data2['no'],
'source'=> $data2['source'],
'destination'=> $data2['destination']));
}
}
$e=0;
for ($a = 0; $a <= 49;)
{
for ($i = 0; $i <= 9; $i++,$a++) {
$rand = array();
$rand[$i] = $result[$a];
}
echo json_encode($rand[1]);
}
?>

Answer 4

Try with the following:
<?php
include_once ("connection.php");
$query = "SELECT * FROM trying";
$count = 0;
while(true)
{
$data = mysql_query($query." LIMIT ".$count.",10");
$random = rand(1,10);
for($i=1;$i<=$random;$i++)
{
$row = mysql_fetch_array($data);
if($row === false)
{
break 2;
}
}
echo json_encode($row);
$count++;
}
?>

Answer 5

Try this :
<?php
set_time_limit(0);
include_once ("connection.php");
$per = 10;
$start = 0;
$total = 0;
$total_query = mysql_query("SELECT COUNT(*) AS total FROM trying");
if(mysql_num_rows($total_query) == 1) {
$row = mysql_fetch_assoc($total_query);
$total = $row['total'];
$offset = ($start * $per);
$results = array();
while($offset <= $total) {
$tmp = array();
$data_query = mysql_query("SELECT * FROM trying LIMIT ".$offset.",".$per);
while ($row = mysql_fetch_array($data_query)) {
array_push($tmp, array(
'no'=> $row['no'],
'source'=> $row['source'],
'destination'=> $row['destination'])
);
}
array_push($results,$tmp[rand(0,9)]);
unset($tmp);
$start++;
$offset = ($start * $per);
}
echo json_encode($results);
} else {
die("No records found.");
}
?>