But I want to show you a bit more about it.[Read more...]
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Many out there will have different ideas about this, some using
procs, some using a function, others using a shell script. Well I
didn’t want to spend much time on it so decided a
group_concat(concat would be enough.
There is no genius, rather laziness :) but what if you have a hundred databases and you want to drop them all?
mysql Thu Mar 3 13:50:06 2011 > pager sed 's/,/ /g' PAGER set to 'sed 's/,/ /g'' mysql Thu Mar 3 13:50:32 2011 > select group_concat(concat('drop database ',SCHEMA_NAME,';')) from information_schema.schemata where SCHEMA_NAME !='mysql' and SCHEMA_NAME !='information_schema'; …[Read more...]
In my opinion, one of the best things that happened to Planet MySQL
lately, is Explain Extended, a blog by Alex Bolenok (also
known as Quassnoi on Stackoverflow).
I never had the pleasure of meeting Alex in person, but his articles are always interesting and of high quality, and the SQL wizardry he pulls off is downright inspiring. I really feel humbled by the creativity of some of his solutions and …
I just read SQL: Ranking without self join, in which
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 …
Abstract - As described by Walter Heck, MySQL database size
can be visualized using Google
Charts. With a minor code improvement the URL for the chart
can be obtained twice as fast. With some more modification, the
number of lines can be cut down resulting in a function that is
half as long.
Hi!It's been a while since I posted - I admit I'm struggling for a bit to balance time and attention to the day job, writing a book, preparing …
After stepping off of the
for calculating quantiles I figured it would be
nice to find a better way to calculate the median too.
I previously wrote on how to calculate the median using
GROUP_CONCAT(), but I think that this is a better
SELECT AVG(length) AS median -- take the average of left and right median
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
SELECT SUM(g1.r) sr
, g2.length l
, SUM(g1.r)/(SELECT COUNT(*) FROM film) p
FROM (SELECT …
Yesterday, I was on the freenode ##pentaho irc channel when
Chaves asked me how to calculate the Nth percentile in MySQL. He saw a
solution somewhere using subqueries, but wasn't too happy about
A while ago I wrote about calulating the median in MySQL, and it turns out the Nth percentile can be calculated using a similar, single-pass approach, not relying on subqueries, …
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