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Displaying posts with tag: hack (reset)
MySQL command line pager & mysmartpager

Few days back, Baron re-introduced MySQL's command line pager command and described some cool tricks with maatkit's mk-visual-explain (one of my favorite tools). Soon after reading it, I wished if it was possible to describe regex based (on query) paging.

I have written a small hack, christened mysmartpager, that can actually do regex based paging for you.

The idea is simple, write a relay that will redirect the output based on to the desired pager. The problem was complex, there was no direct way of getting to know the original query. There are a couple of indirect ways of doing so, but of course with hurdles:

  • Run mysql client with --xml option: This will print the output of each command in xml and the command itself is included in the xml. The downside was not many pagers (including …
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MySQL Percentile aftermath: Calculating all quantiles

Are you getting fed up yet with my posts on calculating percentiles? Well, I'm sorry but I'm not quite finished.

Here's a simple, fast method to calculate the specified number of quantiles:


-- set the number of quantiles, for exmple:
-- quartiles: 4
-- deciles: 10
-- percentiles: 100

SET @quantiles:=4; -- select quartiles

-- calculate all quantiles
--
--
SELECT amount AS metric
, @n DIV (@c DIV @quantiles) AS quantile
, @n AS N
FROM sakila.payment
CROSS JOIN (
SELECT @n:=0 -- rownumber
, @c:=COUNT(*) …
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