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    <p>I think an agreeable solution would be to use an asymptotic function (1/x) in combination with weighting.</p> <p>The following has been tested:</p> <pre><code>SELECT *, (Rand()*10 + (1/(max_id - id + 1))) AS weighted_random FROM tbl1 ORDER BY weighted_random DESC LIMIT 4 </code></pre> <p>If you want to get the max_id within the query above, just replace max_id with:</p> <pre><code>(SELECT id FROM tbl1 ORDER BY id DESC LIMIT 1) </code></pre> <p><strong>Examples:</strong></p> <p>Let's say your max_id is 1000 ...</p> <p>For each of several ids I will calculate out the value:</p> <p>1/(1000 - id + 1) , which simplifies out to 1/(1001 - id):</p> <p><em>id: 1000</em></p> <p>1/(1001-1000) = 1/1 = 1</p> <p><em>id: 999</em></p> <p>1/(1001-999) = 1/2 = .5</p> <p><em>id: 998</em></p> <p>1/(1001-998) = 1/3 = .333</p> <p><em>id: 991</em></p> <p>1/(1001-991) = 1/10 = .1</p> <p><em>id: 901</em></p> <p>1/(1001-901) = 1/100 = .01</p> <p>The nature of this 1/x makes it so that only the numbers close to max have any significant weighting. </p> <p>You can see a graph of + more about asymptotic functions here:</p> <p><a href="http://zonalandeducation.com/mmts/functionInstitute/rationalFunctions/oneOverX/oneOverX.html" rel="nofollow">http://zonalandeducation.com/mmts/functionInstitute/rationalFunctions/oneOverX/oneOverX.html</a></p> <p>Note that the right side of the graph with positive numbers is the only part relevant to this specific problem.</p> <p><strong>Manipulating our equation to do different things:</strong></p> <p>(Rand()*a + (1/(b*(max_id - id + 1/b))))</p> <p>I have added two values, "a", and "b"... each one will do different things:</p> <p>The larger "a" gets, the less influence order has on selection. It is important to have a relatively large "a", or pretty much <em>only</em> recent ids will be selected.</p> <p>The larger "b" gets, the more quickly the asymptotic curve will decay to insignificant weighting. If you want more of the recent rows to be weighted, I would suggest experimenting with values of "b" such as: .5, .25, or .1.</p> <p>The 1/b at the end of the equation offsets problems you have with smaller values of b that are less than one.</p> <p><strong>Note:</strong></p> <p>This is not a very efficient solution when you have a large number of ids (just like the other solutions presented so far), since it calculates a value for each separate id.</p>
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    1. POWeighted randomness. How could I give more weight to rows that have just been added to the database?
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    1. POWeighted randomness. How could I give more weight to rows that have just been added to the database?
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    1. CO`(Rand()*10 + (1/(max_id - id + 1)))` <- can you describe exactly wht this does? Also, would increasing the "10" here make it more likely that older rows are retrieved, or is it the other way around?
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    2. CO@oxo: Just added some explanations and examples above. Please let me know if I can clarify anything.
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    3. COYour explanation needs to be upvoted a million times. Thanks for clarifying.
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