ORDER BY RAND() not random

ade234uk

I have noticed that using ORDER BY RAND() does give me random images, however I am getting some of the same images appear so of course this is not really random. How do I go about displaying true random images.

I don't have any images stored in the DB they are just URLS that point to the images.

laserlight

You might want to read the sticky: Fast Random Results - "ORDER BY RAND()" is bad.

That said, just because the same images appear from time to time does not mean that it is "not really random" (the fact that it is pseudo-random means that it is "not really random"). For example, if you select marbles from a bag at random, with replacement, eventually you will select the same marble more than once.

Weedpacket

If you have three images then you have a one-in-three chance of picking image 1 on the first try. Then you have a one-in-three chance of picking image 1 on the second try: so your chances of picking image 1 twice in a row are one in nine - better than 10%. The same goes for images 2 and 3, so the chances of picking any image twice in a row would be three in nine - or one in three.

If you pick three images there are 3×3×3=27 ways of doing that; but the three images would only be different in 6 of them, so you have a better than 77% chance of having repeats.

And of course if you pick four images then repeats are inevitable.

If there are fifty images in the collection then chances are good there'll be a repeat within the first ten selections.