Using MySQL PHP: select random row based on weight

Article describes algorithm of random row selection based on weight, so some rows will be selected more often than other. Article includes sample codes, so I hope will bу helpful to somebody.
Do not hesitate to leave comments if you have ideas how to improve the algorithm.

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Using MySQL: select random row, but fast

Random rows selection may be slow and there are several commonly used solutions to solve this problm could be googled. In my article I am trying to review a few algorithms and to describe benefits and limitations of them.
Let me know if I have missed some good algorithm.

Read complete article: Using MySQL: select random row, but fast