Let's say I've got a mySQL database: two columns: ID and names, with 100 rows.
What I'd like to do is pick out say 10 names - with no repeats - and display them in random order.
Using this code, I can pick out just one name...
<?php
include('connection.php');
$rand = rand(1, 100);
$sql = "SELECT * FROM names WHERE ID=$rand";
$result = mysql_query($sql, $sandbox);
while ($row = mysql_fetch_array ($result))
{
$name1 = $row['Name'];
echo $name1 . "<br>";
}
?>
... what would be the best code to get my 10 random nonrepeating names?
Depending on the number of rows in the table, you probably don't want to do ORDER BY RAND() as suggested by 4 other people for performance reasons:
The ORDER BY RAND() operation actually re-queries each row of your table, assigns a random number ID and then delivers the results. This takes a large amount of processing time for table of more than 500 rows.
The recommended approach extends your original idea to get 10 IDs and do a simple select query for those.
If they're sequential, you can just generate a random in that range, or retrieve all the IDs, shuffle them and request the first 10 values.
There are some other suggestions in response to this question.
The easiest way (and fastest for the database) would be to generate ten unique numbers using range and shuffle functions, and then create a query with the IN clause:
$numbers = range(1, 100);
shuffle($numbers);
$numbers = implode( ', ', array_slice($numbers, -10) );
$sql = "SELECT * FROM names WHERE ID IN ($numbers)";
// example query:
// SELECT * FROM names WHERE ID IN (63, 76, 69, 59, 9, 84, 60, 18, 23, 62)
$sql = "SELECT DISTINCT id, name FROM names ORDER BY RAND() LIMIT 10";
You will want to use ORDER BY RAND()
$sql = "SELECT * FROM names ORDER BY RAND() LIMIT 10";
$result = mysql_query($sql, $sandbox);
while ($row = mysql_fetch_array ($result)){
try this :
SELECT DISTINCT * FROM names ORDER BY RAND() LIMIT 10
Related
I have some PHP code, which returns all records from my database. I need 10 results on each page. How to paginate the results? Dunno how to write a piece of code responsible for displaying page numbers...
<?php
$query = $link->query("SELECT * FROM news WHERE category='rhythmix' ORDER BY subject DESC");
while($output = $query->fetch_assoc()){
$text = $output['news'];
$text = str_replace('[video]','<div class="video-container">',$text);
$text = str_replace('[/video]','</div>',$text);
$text = str_replace('[media]','<center>',$text);
$text = str_replace('[/media]','</center>',$text);
$embera = new \Embera\Embera();
echo $embera->autoEmbed($text);
}
?>
Add LIMIT to your query in this way:
SELECT *
FROM news
WHERE category='rhythmix'
ORDER BY subject DESC
LIMIT 0, 10;
The first number (0) is the start position on the resulset and the second one (10) is how many results you want to show (the offset).
To show the second page:
...LIMIT 10, 10
If you always want to show 10 results you just need to to add 10 to the first number of the LIMIT.
Change your query to read
$query = $link->query("SELECT * FROM news WHERE category='rhythmix' ORDER BY subject DESC LIMIT 0, 10");
To display the first 10 rows. The next set of 10 rows can be shown using
...LIMIT 10, 10");
and so on. . .
I need to run an ORDER BY RAND query and then sort the resulting data set numerically. In other words I want a random set of data (in this case 7 numbers), but then I need to sort those 7 results numerically.
After this code runs:
if ($today == "Oct 31") {
$dayList = "halloween";
$stmt = $pdo->query("SELECT `rand` FROM `jukebox2014`
WHERE `class` = '$dayList' ORDER BY RAND() LIMIT 7");
}
I need to sort the 7 results.
Any ideas?
Thanks.
As simple as:
SELECT `rand`
FROM (
SELECT ... ORDER BY RAND() LIMIT 7
)
ORDER BY `rand`
Not that ORDER BY RAND() LIMIT 7 is a rather inefficient method to select random data; more efficient methods will depend on your exact data. Search Stackoverflow for many questions regarding this topic.
I think this is what you mean.
$new = array();
foreach ($results as $result) {
$new[] $result['rand'];
}
$sorted = ksort($new);
I've been looking for this for a while but with no success.
I am trying to implement a recomendation bar, for example like in youtube, when you are seeing a video it shows the list or recommended videos on the right.
At this moment I am using this method:
$offset_result = mysql_query( " SELECT FLOOR(RAND() * COUNT(*)) AS `offset` FROM `$tablename` ");
$offset_row = mysql_fetch_object($offset_result );
$offset = $offset_row->offset;
$result_rand = mysql_query( " SELECT * FROM `$tablename` LIMIT $offset, 9 " );
This works fine, but sometimes doesn't show any result, and the problem is also that its not completely random, because it shows for example the first ID as 200, so the next result will be id 201 and then 202 and so.
I would like to know if there is a way to show this 9 randon results, for example 1º result id 500, 2º result id 10, 3º result id 788, etc etc?
Thank you
Not entirely sure this answers what you are looking for, but try:
$result_rand = mysql_query("SELECT * FROM " . $tablename . " ORDER BY RAND() LIMIT 9");
You can use php rand() function to create 5 numbers and save them in an array:
http://php.net/manual/en/function.rand.php
<?php
$rand_array = array();
for($i=1;$i<5;$i++) {
$rand_array[$i] = rand(0,500);
}
?>
and after that create a query with every int with a foreach loop and work with your data.
<?php
foreach ($rand_array as $integer) {
$q = "SELECT * from $tablename WHERE id='$integer';";
}
?>
Does this helps?
First you should use mysqli_ functions instead of mysql_ because the latter is deprecated. Second use order by rand() to get random rows:
$rand_result = mysqli_query( "SELECT * FROM $tablename ORDER BY RAND() LIMIT 9;" );
UNTESTED:
SELECT id, #rownum:=#rownum+1 AS rownum, name
FROM users u,
(SELECT #rownum:=0) r
THis will give a unique number to each row in sequence. Now if you create a temp table with 9 random numbers between 1 and count(*) of your table and JOIN those two together...
Not sure about performance but seems like it might be faster than Rand and order by since I only need 9 random numbers
I have a problem selecting 6 random friends
This is the query I've got so far:
$result = num_rows("SELECT * FROM friends WHERE member_id = '".$_SESSION['userid']."'");
if($result >= 6) {
$f_num = 6;
} else {
$f_num = $result;
}
for($i = 1; $i <= $f_num; $i++) {
$q_get_member_friends = mysql_query("SELECT * FROM friends WHERE member_id = '".$_SESSION['userid']."' ORDER BY rand() LIMIT 1");
$r_get_member_friends = mysql_fetch_array($q_get_member_friends);
echo $r_get_member_friends['friend_with'];
}
I want to select 6 random friends if the logged in user has more or equal to 6 friends
Stuck on this for a while now :/
Thanks for any help :)
If you use:
SELECT *
FROM friends
WHERE member_id = '".$_SESSION['userid']."'
ORDER BY rand()
LIMIT 6
If the person only has 3 friends, the query will only show those three - it doesn't mean that the query will always return six rows.
The best way I've found to select any number of random records is with OFFSET in the query.
Let's say you want 6 random records, so I'll borrow from an answer above and count the total number of friends in the database.
$sql = mysql_query("SELECT COUNT(*) AS total FROM friends WHERE member_id='". $_SESSION['userid'] ."'");
$get_count = mysql_fetch_array($sql); // Fetch the results
$numfriends = $get_count['total']; // We've gotten the total number
Now we'll get the 6 random records out of the total above (hopefully it's > 6),
$query = mysql_query("SELECT * FROM friends WHERE member_id='". $_SESSION['userid'] ."' LIMIT 6 OFFSET " . (rand(0, $numFriends));
while ($rows = mysql_fetch_array($query))
{
/// show your $rows here
}
Using OFFSET may not be the best or most efficient, but it's worked for me on large databases without bogging them down.
Never mind, I figured it out :)
Had to use while not for :'D
First select the number of friends that the user has:
"SELECT COUNT(*) as numFriends FROM friends WHERE member_id='".$_SESSION['userid']."'
...put that into a variable, let's call it "$numFriends"
Then:
for($z=0;$z<6;$z++)
{
$randomFriendIndex = rand(1,$numFriends);
//Get the friend at that index
}
change limit 1 to limit 6 on the eighth line.
Instead of SELECT * at the beginning, try SELECT COUNT(*) and use the actual return value instead of num_rows().
Your loop could generate duplicates. I would suggest trying OMG Ponies answer.
There is a whole chapter about random selection in the book SQL Antipatterns.
I want to show a random record from the database. I would like to be able to show X number of random records if I choose. Therefore I need to select the top X records from a randomly selected list of IDs
(There will never be more than 500 records involved to choose from, unless the earth dramatically increases in size. Currently there are 66 possibles.)
This function works, but how can I make it better?
/***************************************************/
/* RandomSite */
//****************/
// Returns an array of random site IDs or NULL
/***************************************************/
function RandomSite($intNumberofSites = 1) {
$arrOutput = NULL;
//open the database
GetDatabaseConnection('dev');
//inefficient
//$strSQL = "SELECT id FROM site_info WHERE major <> 0 ORDER BY RAND() LIMIT ".$intNumberofSites.";";
//Not wonderfully random
//$strSQL = "SELECT id FROM site_info WHERE major <> 0 AND id >= (SELECT FLOOR( COUNT(*) * RAND()) FROM site_info ) ORDER BY id LIMIT ".$intNumberofSites.";";
//Manual selection from available pool of candidates ?? Can I do this better ??
$strSQL = "SELECT id FROM site_info WHERE major <> 0;";
if (is_numeric($intNumberofSites))
{
//excute my query
$result = #mysql_query($strSQL);
$i=-1;
//create an array I can work with ?? Can I do this better ??
while ($row = mysql_fetch_array($result, MYSQL_NUM))
{
$arrResult[$i++] = $row[0];
}
//mix them up
shuffle($arrResult);
//take the first X number of results ?? Can I do this better ??
for ($i=0;$i<$intNumberofSites;$i++)
{
$arrOutput[$i] = $arrResult[$i];
}
}
return $arrOutput;
}
UPDATE QUESTION:
I know about the ORDER BY RAND(), I just don't want to use it because there are rumors it isn't the best at scaling and performance. I am being overly critical of my code. What I have works, ORDER BY RAND() works, but can I make it better?
MORE UPDATE
There are holes in the IDs. There is not a ton of churn, but any churn that happens needs to be approved by our team, and therefore could handled to dump any caching.
Thanks for the replies!
Why not use the Rand Function in an orderby in your database query? Then you don't have to get into randomizing etc in code...
Something like (I don't know if this is legal)
Select *
from site_info
Order by Rand()
LIMIT N
where N is the number of records you want...
EDIT
Have you profiled your code vs. the query solution? I think you're just pre-optimizing here.
If you dont want to select with order by rand().
Instead of shuffeling, use array_rand on the result:
$randKeys = array_rand($arrResult, $intNumberofSites);
$arrOutput = array_intersect_key(array_flip($randKeys), $arrResult);
edit: return array of keys not new array with key => value
Well, I don't think that ORDER BY RAND() would be that slow in a table with only 66 rows, but you can look into a few different solutions anyway.
Is the data really sparse and/or updated often (so there are big gaps in the ids)?
Assuming it's not very sparse, you could select the max id from the table, use PHP's built-in random function to pick N distinct numbers between 1 and the max id, and then attempt to fetch the rows with those ids from the table. If you get back less rows than you picked numbers, get more random numbers and try again, until you have the number of rows needed. This may not be particularly fast either.
If the data is sparse, I would set up a secondary "id-type" column that you make sure is sequential. So if there are 66 rows in the table, ensure that the new column contains the values 1-66. Whenever rows are added to or removed from the table, you will have to do some work to adjust the values in this column. Then use the same technique as above, picking random IDs in PHP, but you don't have to worry about the "missing ID? retry" case.
Here are the three functions I wrote and tested
My answer
/***************************************************/
/* RandomSite1 */
//****************/
// Returns an array of random rec site IDs or NULL
/***************************************************/
function RandomSite1($intNumberofSites = 1) {
$arrOutput = NULL;
GetDatabaseConnection('dev');
$strSQL = "SELECT id FROM site_info WHERE major <> 0;";
if (is_numeric($intNumberofSites))
{
$result = #mysql_query($strSQL);
$i=-1;
while ($row = mysql_fetch_array($result, MYSQL_NUM)) {
$arrResult[$i++] = $row[0]; }
//mix them up
shuffle($arrResult);
for ($i=0;$i<$intNumberofSites;$i++) {
$arrOutput[$i] = $arrResult[$i]; }
}
return $arrOutput;
}
JPunyon and many others
/***************************************************/
/* RandomSite2 */
//****************/
// Returns an array of random rec site IDs or NULL
/***************************************************/
function RandomSite2($intNumberofSites = 1) {
$arrOutput = NULL;
GetDatabaseConnection('dev');
$strSQL = "SELECT id FROM site_info WHERE major<>0 ORDER BY RAND() LIMIT ".$intNumberofSites.";";
if (is_numeric($intNumberofSites))
{
$result = #mysql_query($strSQL);
$i=0;
while ($row = mysql_fetch_array($result, MYSQL_NUM)) {
$arrOutput[$i++] = $row[0]; }
}
return $arrOutput;
}
OIS with a creative solution meeting the intend of my question.
/***************************************************/
/* RandomSite3 */
//****************/
// Returns an array of random rec site IDs or NULL
/***************************************************/
function RandomSite3($intNumberofSites = 1) {
$arrOutput = NULL;
GetDatabaseConnection('dev');
$strSQL = "SELECT id FROM site_info WHERE major<>0;";
if (is_numeric($intNumberofSites))
{
$result = #mysql_query($strSQL);
$i=-1;
while ($row = mysql_fetch_array($result, MYSQL_NUM)) {
$arrResult[$i++] = $row[0]; }
$randKeys = array_rand($arrResult, $intNumberofSites);
$arrOutput = array_intersect_key($randKeys, $arrResult);
}
return $arrOutput;
}
I did a simple loop of 10,000 iterations where I pulled 2 random sites. I closed and opened a new browser for each function, and cleared the cached between run. I ran the test 3 times to get a simple average.
NOTE - The third solution failed at pulling less than 2 sites as the array_rand function has different output if it returns a set or single result. I got lazy and didn't fully implement the conditional to handle that case.
1 averaged: 12.38003755 seconds
2 averaged: 12.47702177 seconds
3 averaged: 12.7124153 seconds
mysql_query("SELECT id FROM site_info WHERE major <> 0 ORDER BY RAND() LIMIT $intNumberofSites")
EDIT
Damn, JPunyon was a bit quicker :)
Try this:
SELECT
#nv := #min + (RAND() * (#max - #min)) / #lc,
(
SELECT
id
FROM site_info
FORCE INDEX (primary)
WHERE id > #nv
ORDER BY
id
LIMIT 1
),
#max,
#min := #nv,
#lc := #lc - 1
FROM
(
SELECT #min := MIN(id)
FROM site_info
) rmin,
(
SELECT #max := MAX(id)
FROM site_info
) rmax,
(
SELECT #lc := 5
) l,
site_info
LIMIT 5
This will select a random ID on each iteration using index, in descending order.
There is slight chance, though, that you get less results that you wanted, as it gives no second chance to the missed id's.
The more percent of rows you select, the bigger is the chance.
I would simply use the rand() function (I assume you are using MySQL)...
SELECT id, rand() as rand_idx FROM site_info WHERE major <> 0 ORDER BY rand_idx LIMIT x;
I'm with JPunyon. Use ORDER BY RAND() LIMIT $N. I think you'll get a bigger performance hit from $arrResult having and shuffling so many (unused) entries than from using the MySQL RAND() function.
function getSites ( $numSites = 5 ) {
// Sanitize $numSites if necessary
$result = mysql_query("SELECT id FROM site_info WHERE major <> 0 "
."ORDER BY RAND() LIMIT $numSites");
$arrResult = array();
while ( $row = mysql_fetch_array($result,MYSQL_NUM) ) {
$arrResult[] = $row;
}
return $arrResult;
}