Comments on: How to select the first or last row per group in SQL http://www.xaprb.com/blog/2007/08/21/how-to-select-the-first-or-last-row-per-group-in-sql/ Stay curious! Thu, 09 Feb 2012 20:41:20 +0000 hourly 1 http://wordpress.org/?v=3.2.1 By: Webmaster http://www.xaprb.com/blog/2007/08/21/how-to-select-the-first-or-last-row-per-group-in-sql/#comment-18152 Webmaster Sat, 17 Apr 2010 07:40:34 +0000 http://www.xaprb.com/blog/2007/03/21/how-to-select-the-first-or-last-row-per-group-in-sql/#comment-18152 Here is a great simple and efficient solution to the problem. It's close to just saying FIRST() LAST() in MySQL http://topwebguy.com/first-and-last-in-mysql-a-working-solution/ Here is a great simple and efficient solution to the problem. It’s close to just saying FIRST() LAST() in MySQL

http://topwebguy.com/first-and-last-in-mysql-a-working-solution/

]]> By: Simulating First/Last aggregate functions in MySQL | zonalivre.org http://www.xaprb.com/blog/2007/08/21/how-to-select-the-first-or-last-row-per-group-in-sql/#comment-17100 Simulating First/Last aggregate functions in MySQL | zonalivre.org Mon, 12 Oct 2009 00:17:57 +0000 http://www.xaprb.com/blog/2007/03/21/how-to-select-the-first-or-last-row-per-group-in-sql/#comment-17100 [...] came across an interesting post at Xaprb.com on selecting the first and last row of a group in MySQL.  This solution builds on a comment in [...] [...] came across an interesting post at Xaprb.com on selecting the first and last row of a group in MySQL.  This solution builds on a comment in [...]

]]> By: Scot http://www.xaprb.com/blog/2007/08/21/how-to-select-the-first-or-last-row-per-group-in-sql/#comment-17038 Scot Mon, 28 Sep 2009 21:19:02 +0000 http://www.xaprb.com/blog/2007/03/21/how-to-select-the-first-or-last-row-per-group-in-sql/#comment-17038 I ran into a scenario which required me to use the last row of a group, and after a lot of searching and looking up all the usual methods I came up with one which I thought I'd share incase anyone else does. I did not use any sub-queries or the likes due to how slow they are, but instead made use of the GROUP_CONCAT() function. In my scenario, I had a table which had rows of data for every "minute", each row contained 4 main values I needed: open, close, high, low. I made my query to group this data into 5 minute intervals, such as: 5:00PM, 5:05PM, 5:10PM and so on. The high/low was easily accomplished by MIN/MAX, the open was correct because "group by" returns the first rows "open" value, but obviously "close" was incorrect and I needed the last row of the group. The main method mentioned here did not do me any good due to the large amount of data I was working with, and my solution was simply this (this is not the exact query): ---------------------------- select open, MAX(high), MIN(low), SUBSTRING_INDEX(GROUP_CONCAT(CAST(close as CHAR)), ',', -1) from mytable group by [xyz...] ---------------------------- The group_concat() will return all "close" values within the group seperated by a comma, I used CAST() because the values are FLOAT and would otherwise result in BLOB, lastly the SUBSTRING_INDEX() function was used to retrieve the last item in the string after the final comma. Works like a charm! I ran into a scenario which required me to use the last row of a group, and after a lot of searching and looking up all the usual methods I came up with one which I thought I’d share incase anyone else does.

I did not use any sub-queries or the likes due to how slow they are, but instead made use of the GROUP_CONCAT() function.

In my scenario, I had a table which had rows of data for every “minute”, each row contained 4 main values I needed: open, close, high, low. I made my query to group this data into 5 minute intervals, such as: 5:00PM, 5:05PM, 5:10PM and so on. The high/low was easily accomplished by MIN/MAX, the open was correct because “group by” returns the first rows “open” value, but obviously “close” was incorrect and I needed the last row of the group. The main method mentioned here did not do me any good due to the large amount of data I was working with, and my solution was simply this (this is not the exact query):

—————————-
select
open, MAX(high), MIN(low), SUBSTRING_INDEX(GROUP_CONCAT(CAST(close as CHAR)), ‘,’, -1)

from mytable

group by [xyz...]
—————————-

The group_concat() will return all “close” values within the group seperated by a comma, I used CAST() because the values are FLOAT and would otherwise result in BLOB, lastly the SUBSTRING_INDEX() function was used to retrieve the last item in the string after the final comma.

Works like a charm!

]]> By: Zaman http://www.xaprb.com/blog/2007/08/21/how-to-select-the-first-or-last-row-per-group-in-sql/#comment-14228 Zaman Thu, 21 Feb 2008 05:29:30 +0000 http://www.xaprb.com/blog/2007/03/21/how-to-select-the-first-or-last-row-per-group-in-sql/#comment-14228 This is not helping specially when you are shortening the queries , you are writing in detail but you come to practice you are shorting your only way to explain what are you talking about.. This is not helping specially when you are shortening the queries , you are writing in detail but you come to practice you are shorting your only way to explain what are you talking about..

]]> By: Artem Nosulchik http://www.xaprb.com/blog/2007/08/21/how-to-select-the-first-or-last-row-per-group-in-sql/#comment-13374 Artem Nosulchik Wed, 05 Sep 2007 07:38:34 +0000 http://www.xaprb.com/blog/2007/03/21/how-to-select-the-first-or-last-row-per-group-in-sql/#comment-13374 Thank you. Nice tips! Thank you. Nice tips!

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