Random row from your MySQL table with PHP, alternative to ORDER BY rand()

Jerry Low — Thu, 22 Apr 2010 21:28:04 +0000

Working with MySQL and PHP is awesome. Its one of the best way to manage your data, but once in a while you may want to do some randomizing. One problem I came across recently was how to select a random row from your MySQL table with PHP. Using the ORDER BY rand() method in your query maybe a bit slow so here's what we've got.

The Premade Method

As I mentioned in the beginning. MySQL actually has a premade method that allows you to select a random row by querying for it.

mysql_query("SELECT * FROM table ORDER BY rand() LIMIT 0,1");

This method is great but if you are randomizing from a large table this method is not very efficient and with a high volume of queries it really puts a strain on your DB.

The New Method – Randomizing 1 Entry

Now here's the new solution by selecting a random row with the offset. This method will query exactly to the random entry; thus, making this process much faster.

$query = "SELECT * FROM table"
$num_rows = mysql_num_rows( mysql_query( $query ) );

//Random Number
$rand_row = rand(0, $num_rows – 1);

//Selecting the Random Row
$rand_row = $query .= " LIMIT $rand_row, 1";

Now you can modify the $query line to include your filters and sorting stuff, whatever you need.

The New Method – Randomizing More than 1 Entry

The above method right now can only select a single row. What if you want to randomized more than one item. Here's a method to select multiple items without overlap.

//Set the Amount of Random Rows you want
$rand_amount = 5;

$query = "SELECT * FROM table"
$num_rows = mysql_num_rows( mysql_query( $query ) );

//Make sure you have more than the amount of random count you want
if ($num_rows <= $rand_amount) {

//An Array of Numbers Choosen
$rand_array = array();

//Do IT!!
for ($i = 1; $i >= $rand_amount; $i++ ) {
do {
$rand_added = FALSE;
$rand_num = rand(0, $num_rows – 1);

//Should We Add to Array
if (!in_array($rand_num, $rand_array)) {

$rand_array[] = $rand_num;
$rand_added = TRUE;
}

} while (!$rand_added);
}

//You now have a set of random row numbers to choose from
//Display The Result of What you have
foreach ($rand_array as $rand_num) {
$new_query = $query . " LIMIT $rand_num, 1";

//Displaying What you have
$current_row = mysql_fetch_array( mysql_query( $new_query ) );
}
}

To be honest you can use the multiple randomizer and just set the random amount to 1 but the other method saves you like 20 lines of code. Imagine how much faster that could be!

CrankBerry Blog » Random

Random row from your MySQL table with PHP, alternative to ORDER BY rand()

The Premade Method

The New Method – Randomizing 1 Entry

The New Method – Randomizing More than 1 Entry