Comments on: Simulating First/Last aggregate functions in MySQL

By: Joao

Joao — Sat, 17 Apr 2010 14:31:28 +0000

I’ve just tried your approach and indeed it’s more efficient. Thanks for sharing!

By: webmaster

webmaster — Sat, 17 Apr 2010 08:12:30 +0000

You can get results like that but you are sorting (order-ing) in calculated colums which will not be efficient with large tables.
Here is a solution that is simple elegant and uses efficiently indexes etc.
The text behid the link is specifically only about this solution of a FIRST and LAST aggragating functions wiht GROUP BY in MySQL:
http://topwebguy.com/first-and-last-in-mysql-a-working-solution/

By: Joao

Joao — Sat, 28 Nov 2009 14:28:03 +0000

But how do you guarantee sort order ? That’s the bit I couldn’t figure out. Does “datetime as `desc`” somehow make it happen, or is it something that can be implemented inside the UDF ?

By: Arnold Daniels

Arnold Daniels — Sat, 28 Nov 2009 13:56:07 +0000

Nice little hack .

You could do this with a MySQL UDF though. Like the above function you need to pass the field with the value as well as the field to order by.

SELECT agg_last(close, datetime AS `desc`) FROM …

By: Joao

Joao — Fri, 20 Nov 2009 12:23:21 +0000

Not sure you can do this as a function using the same underlying logic.

My first approach was to create an aggregate UDF, but that didn’t work because you can’t guarantee the order of data going into the udf.

By: stephen

stephen — Thu, 19 Nov 2009 17:58:45 +0000

I am trying to turn this into a function, but it won’t work. Please, correct me.

DELIMITER $$

DROP FUNCTION IF EXISTS `test`.`last`$$
CREATE FUNCTION `test`.`last`(f1 varchar(12),f2 varchar(12)) RETURNS varchar(12) CHARSET latin1
return substring_index(group_concat(f1 order by f2 desc),’,',1);

DELIMITER ;

By: Joao

Joao — Mon, 26 Oct 2009 10:35:16 +0000

Sure. When you’re done send me the link so I can see it.

By: Polprav

Polprav — Thu, 22 Oct 2009 21:30:01 +0000

Hello from Russia!
Can I quote a post in your blog with the link to you?