Re: Rand() Emulation

On Wednesday 25 June 2003 00:19, Gerard Samuel wrote: > Im probably not making myself clear. > Ultimately, my goal is to emulate mysql's -> > SELECT * FROM TABLE ORDER BY RAND() LIMIT (X) > > for other databases that do not support RAND(). So using variations of > php's rand(), wouldn't make sense, > as it only picks one value out of a range of values, that are numerical > in nature. > > But here is an idea, that Im thinking about, but haven't gotten to the > code as yet. > 1. In the tables that I want random values from, create a "rand" > column, that contains incremental numerical values for each row. > 2. select the the maximum number from the rand column. > 3. Assume that there are no gaps between 0 and this max number. > 4. Create an array of numbers with values between 0 and max number. > 5. Use array_rand() to "randomly" choose (x) values from the array > created in step 4. (I may choose maybe > a 1 or 2 values more than whats required, just in case of gaps between 0 > and max number in step 3). > 6. Use these randomly choosen values to select from the database as > random rows. Here's a trick taken from Paul DuBois' MySQL book: SELECT ..., some_column * 0 + RAND() as rand_col FROM ... ORDER BY rand_col; I've not tried it myself so YMMV. -- Jason Wong -> Gremlins Associates -> www.gremlins.biz Open Source Software Systems Integrators * Web Design & Hosting * Internet & Intranet Applications Development * ------------------------------------------ Search the list archives before you post http://marc.theaimsgroup.com/?l=php-db ------------------------------------------