""Richard Lynch"" <ceo@xxxxxxxxx> wrote in message news:42333.67.184.124.249.1117826333.squirrel@xxxxxxxxxxxxxxxx > > How do you generate a list of 50 random unique IDs in the first place? > By using the SQL function to create those randoms > How to you guarantee that all those IDs are in the database? > No need for that. When you do 'order by rand()' SQL understand that you are adding an extra, unnamed column which contains the value of the function rand(). Since rand() is, of course, random, the records are ordered in arbitrary ways. Then you take the first 50 or whatever of those randomly sorted records. The problem is that to do so, it will have to read sequentially all of the table to assign each record a random number, and then sort those. It works for short tables, it is a killer for big ones. Once upon a time, on a table with an autoincrement field, I first fetched the minimum and maximum current value of that autoincrement field. Then I did individual one-record selects (limit 1) with the key equal or greater to a set of randoms created within those minimum and maximum value. Since two randoms could produce the same record, I checked the key of each resulting record against an array which had the primary keys as key. When the count() of that array reached the number of records I wanted, I was done. This was for a very little subset of a really large table and in those circumstances it was faster than the other way. satyam > What if a record gets deleted? > > I suppose *ONE* option to try would be to just get the full result set, > and then use PHP's mt_rand() to skip forward/backward a random number of > records, using something like: > > //untested code > $count = mysql_num_rows($result); > $ids = array(); > while (count($ids) < 50 && count($ids) < $count){ > $random = mt_rand(0, $count - 1); > mysql_data_seek($result, $random); > $id = $result['id']; > //Note use of $id as key, so duplicates are ignored. > $ids[$id] = $id; > } > > This will perform MISERABLY when your number of records is closer to 50. > > It would be okay only if all searches result in tons and tons of records. > > One does have to wonder: > If the user has put in multiple search criteria, why order randomly? Why > not put best matches first? > > -- > Like Music? > http://l-i-e.com/artists.htm -- PHP General Mailing List (http://www.php.net/) To unsubscribe, visit: http://www.php.net/unsub.php
