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Displaying posts with tag: User defined variable (reset)

MySQL User Defined Variables
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When I have discovered MySQL User-defined variables at the first time, I didn’t pay much attention to them and didn’t realize their strength. At first, one can think that they are just one of the many unnoticed MySQL features. Well, I was wrong. Here, I will try to summarize their strength, though I think there is […]

MySQL: Another Ranking trick
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I just read SQL: Ranking without self join, in which Shlomi Noach shares a nice MySQL-specific trick based on user-defined variables to compute rankings.

Shlomi's trick reminds me somewhat of the trick I came across little over a year ago to caclulate percentiles. At that time, several people pointed …

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A fast, single pass method to calculate the median in MySQL
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After stepping off of the GROUP_CONCAT() solution for calculating quantiles I figured it would be nice to find a better way to calculate the median too.
Solution
I previously wrote on how to calculate the median using GROUP_CONCAT(), but I think that this is a better way:


SELECT AVG(length) AS median -- take the average of left and right median
, …




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Calculating Percentiles with MySQL, Round 2
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My previous post on calculating percentiles with MySQL generated some comments and good discussion. In particular, I got some very interesting comments from Vladimir.

Basically, Vladimir was doubtful whether the GROUP_CONCAT() solution would be optimal in comparison to a JOIN. His proposal is to solve it like this:


SELECT SUM(g1.r) sr
, g2.length l
, SUM(g1.r)/(SELECT COUNT(*) FROM film) p
FROM (SELECT …






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