Doing a while / loop to get 10 random results - php

Question

Hello i'm trying to make a tag script for my website so each time a search engine comes to my website 10 different tags will show on my website.
These tags will be grabbed from the db.
So at the minute i have coded it so it grabs only one. ( because i don't know how to do a while )
Like so
$sql = "SELECT tagname FROM tags ORDER BY rand() LIMIT 10";
$result = mysql_query($sql);
$row = mysql_fetch_object($result);
echo "<a href='index.php'>" .$row->tagname. " </a>";
Is there anyway i can add a while to that so it does it 10 times ? E.g use the same echo but print out 10 results instead of the 1 .... i have changed the limit from 1 to 10 but that did not work... still showing one...

Answer 1

Please, stop using ORDER BY RAND(). Just stop. This operation has complexity of n*log2(n), which means that the time spent on query would grow "
entries | time units
-------------------------
10 | 1 /* if this takes 0.001s */
1'000 | 300
1'000'000 | 600'000 /* then this will need 10 minutes */
If you want to generate random results, create a stored procedure, which generates them. Something like this (code taken from this article, which you should read):
DELIMITER $$
DROP PROCEDURE IF EXISTS get_rands$$
CREATE PROCEDURE get_rands(IN cnt INT)
BEGIN
DROP TEMPORARY TABLE IF EXISTS rands;
CREATE TEMPORARY TABLE rands ( tagname VARCHAR(63) );
loop_me: LOOP
IF cnt < 1 THEN
LEAVE loop_me;
END IF;
SET cnt = cnt - 1;
INSERT INTO rands
SELECT tags.tagname
FROM tags
JOIN (SELECT (RAND()*(SELECT MAX(tags.id) FROM tags)) AS id) AS choices
WHERE tags.id >= choices.id
LIMIT 1;
END LOOP loop_me;
END$$
DELIMITER ;
And to use it, you would write:
CALL get_rands(10);
SELECT * FROM rands;
As for executing it all on PHP side, you should stop using the ancient mysql_* API. It is more than 10 years old and no longer maintained. Community has even begun process for deprecating them. There should not be any more new code written with mysql_* in 2012. Instead you should use PDO or MySQLi. As for how to write it (with PDO):
// creates DB connection
$connection = new PDO('mysql:host=localhost;dbname=mydb;charset=UTF-8',
'username', 'password');
$connection->setAttribute(PDO::ATTR_EMULATE_PREPARES, false);
// executes the procedure and creates select statement
$connection->exec('CALL get_rands(10)');
$statement = $connection->query('SELECT * FROM rands');
// performs query and collects all the info
if ($statement->execute())
{
$tags = $statement->fetchAll(PDO::FETCH::ASSOC);
}
Update
If the requirement is to get not only 10 random results, but actually 10 UNIQUE random results, then it would require two changes to the PROCEDURE:
The temporary table should enforce the uniqueness of entries:
CREATE TEMPORARY TABLE rands ( tagname VARCHAR(63) UNIQUE);
It also might make sense to collect just IDs and not the values. Esspecially if what you are looking for are 10 unique articles, not just tags.
When inserting a duplicate value is found, the cnt counter should not decrease. This can be ensured by adding a HANDLER (before definition of LOOP), which would "catch" the raised warning, and adjust the counter:
DECLARE CONTINUE HANDLER FOR SQLSTATE '23000' SET cnt = cnt + 1;

Answer 2

Note, read before the real answer: for the ones that keep downvoting this answer. Read the title (that starts with "Doing a while") and the final part, the question ("Is there anyway i can add a while to that so it does it 10 times ?"). This answer is about iterating the result set, not about the usage of the RAND function! The query doesn't even appear in my answer, and I am also suggesting a different approach at the end:
you just need to wrap your call to mysql_fetch_object in a loop
$result = mysql_query($sql);
while ($row = mysql_fetch_object($result))
{
echo "<a href='index.php'>" .$row->tagname. " </a>";
}
Later edit
Other considerations would be:
if the table hold a very big amount of data (but it doesn't seem that it will) order by rand() can have a bad effect on the performance
consider using pdo (or at least mysqli)
you should have some error handling even if the query seems to be
perfect, at least
if (!$result)
{
echo mysql_error();
die;
}

Answer 3

You are fetching only one of them
You need to fetch all of them one by one in a while
$sql = "SELECT tagname FROM tags ORDER BY rand() LIMIT 10";
$result = mysql_query($sql);
while($row = mysql_fetch_object($result)) {
echo "<a href='index.php'>" .$row->tagname. " </a>";
}