Re: How to find random records in a subset?

Brian Dunning wrote:

I am using a routine to find 50 random records in a large MySQL

how random does it need to be? if *psuedo* (nobody start on the computer random is not really random argument - go watch "What the bleep do we know?" instead) random is okay maybe you could define a list of [funky/weird] ORDER BY subclauses and randomly pick one to add to you sql query. by funky/weird I meaning using multiple comlumn and direction indentifiers in unusual combinations. to increase the psuedo randomness you could potentially use a randomized FIRST declaration (or OFFSET in MySQL) - rather like you would with a pagination routine. but thats dependent on the size of the constrained resultset you get. or alternatively, copy the data offline. run a "nice -19'd" script to generate a batch of random 50 item sets. then let the online site use the generated sets ... item [ids] in a set not found in the live DB could be filled in by a query using the same where clause (but without the randomization) and with a relevant FIRST, SKIP declaration for the 'fill', which assuming your tables are indexed properly should be fast. hope thats understandable. rgds, Jochem

database (about a million records) where I generate a list of 50 random unique ID's, and then use MySQL's "in" command to find them. I can't use "order by rand()" due to its performance hit. But I have to take it one more step: I want to first limit my found set to those matching a different search criteria, and then find 50 of those. Anyone? Can this be done all within MySQL, or is it going to require some humongo PHP arrays?