What is the best algorithm to control the probability of a random sample from an array?

Question

Database

Greetings!
There is such an interesting task that my programmer can’t master something in any way:
on my website (construction portal) they decided to introduce something like their own teaser network ...
writing it was no problem, but here’s where the stop happened: the
probability of showing We decided to make ads the product of ctr and the cost per click entered by the advertiser (according to the Google system, the intersection of a high cost per click and a high quality of an ad wins) ...
But here's how to effectively and correctly implement such ad selection control, until we could finish it ...
I would be grateful for any advice! !! :)

Answer 1

If the ad base in MySQL and ads is not very large, then it can be something like this:
SELECT ... ORDER BY ctr * price + RAND ()
where x is some coefficient

Answer 2

Let me suggest a heavy mathematical solution:
1) normalization and at the same time definition of RND() boundaries for each declaration: ( LEFT[i]; LEFT[i+1] )
NORM=0
for i=0 to N-1
LEFT[i] = NORM
NORM = NORM + CTR[i]*PRICE[i]
2) work
ADV_ID = GET_i_BY_LEFT_BORDER( RND()*NORM )

Answer 3

ORDER BY RAND () is the simplest, but very slow for large tables, this should also be taken into account.