Comments on: SQL trick: overcoming GROUP_CONCAT limitation in special cases http://code.openark.org/blog/mysql/sql-trick-overcoming-group_concat-limitation-in-special-cases Blog by Shlomi Noach Wed, 01 Feb 2012 20:47:51 +0000 hourly 1 http://wordpress.org/?v=3.3.1 By: marcin http://code.openark.org/blog/mysql/sql-trick-overcoming-group_concat-limitation-in-special-cases/comment-page-1#comment-57926 marcin Mon, 07 Nov 2011 14:22:06 +0000 http://code.openark.org/blog/?p=2580#comment-57926 you're right you're right

]]> By: shlomi http://code.openark.org/blog/mysql/sql-trick-overcoming-group_concat-limitation-in-special-cases/comment-page-1#comment-57913 shlomi Mon, 07 Nov 2011 12:27:16 +0000 http://code.openark.org/blog/?p=2580#comment-57913 @marcin, I wrote: "...I will follow the path where I assume I cannot control group_concat_max_len, not even in session scope..." Yes, if you have control, just change group_concat_max_len. This is not always the case. For example, I provide a schema with views which I expect you to install on your server. I cannot change your session variable since I am not the one invoking queries; it is YOU who is invoking queries using my own views. There's a hack around this, as well, and an ugly one as well. @marcin,
I wrote: "...I will follow the path where I assume I cannot control group_concat_max_len, not even in session scope..."

Yes, if you have control, just change group_concat_max_len. This is not always the case. For example, I provide a schema with views which I expect you to install on your server. I cannot change your session variable since I am not the one invoking queries; it is YOU who is invoking queries using my own views. There's a hack around this, as well, and an ugly one as well.

]]> By: marcin http://code.openark.org/blog/mysql/sql-trick-overcoming-group_concat-limitation-in-special-cases/comment-page-1#comment-57909 marcin Mon, 07 Nov 2011 11:54:55 +0000 http://code.openark.org/blog/?p=2580#comment-57909 before executing query try execute SET SESSION group_concat_max_len = 20000 before executing query try execute SET SESSION group_concat_max_len = 20000

]]> By: shlomi http://code.openark.org/blog/mysql/sql-trick-overcoming-group_concat-limitation-in-special-cases/comment-page-1#comment-16004 shlomi Thu, 22 Jul 2010 06:12:45 +0000 http://code.openark.org/blog/?p=2580#comment-16004 @strcmp: for completeness, the trick of CONCAT still makes it more robust, since otherwise you must add you own "," separators between the GROUP_CONCAT parts; should any of them be empty, the manually added separators be invalid. @strcmp: for completeness, the trick of CONCAT still makes it more robust, since otherwise you must add you own "," separators between the GROUP_CONCAT parts; should any of them be empty, the manually added separators be invalid.

]]> By: shlomi http://code.openark.org/blog/mysql/sql-trick-overcoming-group_concat-limitation-in-special-cases/comment-page-1#comment-16003 shlomi Thu, 22 Jul 2010 06:11:13 +0000 http://code.openark.org/blog/?p=2580#comment-16003 @strcmp: wow! Thanks for this @strcmp: wow! Thanks for this

]]> By: strcmp http://code.openark.org/blog/mysql/sql-trick-overcoming-group_concat-limitation-in-special-cases/comment-page-1#comment-16001 strcmp Thu, 22 Jul 2010 05:45:00 +0000 http://code.openark.org/blog/?p=2580#comment-16001 You can use GROUP_CONCAT(IF(actor_id BETWEEN 1 AND 100, last_name, NULL)) instead of GROUP_CONCAT(IF(actor_id BETWEEN 1 AND 100, last_name, '')) to get rid of the extra separators. '' is a normal value that will just be concatenated, NULL will be skipped. You can use GROUP_CONCAT(IF(actor_id BETWEEN 1 AND 100, last_name, NULL)) instead of GROUP_CONCAT(IF(actor_id BETWEEN 1 AND 100, last_name, '')) to get rid of the extra separators. '' is a normal value that will just be concatenated, NULL will be skipped.

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