How can I get better randomization in my sql query?

I am attempting to get a random bearing, from 0 to 359.9.开发者_开发技巧

SET bearing = FLOOR((RAND() * 359.9));

I may call the procedure that runs this request within the same while loop, immediately one after the next. Unfortunately, the randomization seems to be anything but unique. e.g.

Results

358.07

359.15

357.85

I understand how randomization works, and I know because of my quick calls to the same function, the ticks used to generate the random number are very close to one another.

In any other situation, I would wait a few milliseconds in between calls or reinit my Random object (such as in C#), which would greatly vary my randomness. However, I don't want to wait in this situation.

How can I increase randomness without waiting?

I understand how randomization works, and I know because of my quick calls to the same function, the ticks used to generate the random number are very close to one another.

That's not quite right. Where folks get into trouble is when they re-seed a random number generator repeatedly with the current time, and because they do it very quickly the time is the same and they end up re-seeding the RNG with the same seed. This results in the RNG spitting out the same sequence of numbers each time it is re-seeded.

Importantly, by "the same" I mean exactly the same. An RNG is either going to return an identical sequence or a completely different one. A "close" seed won't result in a "similar" sequence. You will either get an identical sequence or a totally different one.

The correct solution to this is not to stagger your re-seeds, but actually to stop re-seeding the RNG. You only need to seed an RNG once.

Anyways, that is neither here nor there. MySQL's RAND() function does not require explicit seeding. When you call RAND() without arguments the seeding is taken care of for you meaning you can call it repeatedly without issue. There's no time-based limitation with how often you can call it.

Actually your SQL looks fine as is. There's something missing from your post, in fact. Since you're calling FLOOR() the result you get should always be an integer. There's no way you'll get a fractional result from that assignment. You should see integral results like this:

187
274
89
345

That's what I got from running SELECT FLOOR(RAND() * 359.9) repeatedly.

Also, for what it's worth RAND() will never return 1.0. Its range is 0 ≤ RAND() < 1.0. You are safe using 360 vs. 359.9:

SET bearing = FLOOR(RAND() * 360);