DROP TABLE IF EXISTS `table`; CREATE TABLE `table` ( `id` tinyint(3) unsigned NOT NULL AUTO_INCREMENT, `text` text COLLATE utf8_unicode_ci NOT NULL, PRIMARY KEY (`id`) ) ENGINE=MyISAM AUTO_INCREMENT=3 DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci; INSERT INTO `table` VALUES ('1', 'Unpacked reserved sir offering bed judgment may and quitting speaking. Is do be improved raptures offering required in replying raillery. Stairs ladies friend by in mutual an no. Mr hence chief he cause. Whole no doors on hoped. Mile tell if help they ye full name. \r\n\r\nLadyship it daughter securing procured or am moreover mr. Put sir she exercise vicinity cheerful wondered. Continual say suspicion provision you neglected sir curiosity unwilling. Simplicity end themselves increasing led day sympathize yet. General windows effects not are drawing man garrets. Common indeed garden you his ladies out yet. Preference imprudence contrasted to remarkably in on. Taken now you him trees tears any. Her object giving end sister except oppose. \r\n\r\nWas justice improve age article between. No projection as up preference reasonably delightful celebrated. Preserved and abilities assurance tolerably breakfast use saw. And painted letters forming far village elderly compact. Her rest west each spot his and you knew. Estate gay wooded depart six far her. Of we be have it lose gate bred. Do separate removing or expenses in. Had covered but evident chapter matters anxious.'); INSERT INTO `table` VALUES ('2', 'Unpacked reserved sir offering bed judgment may and quitting speaking. Is do be improved raptures offering required in replying raillery. Stairs ladies friend by in mutual an no. Mr hence chief he cause. Whole no doors on hoped. Mile tell if help they ye full name. \r\n\r\nLadyship it daughter securing procured or am moreover mr. Put sir she exercise vicinity cheerful wondered. Continual say suspicion provision you neglected sir curiosity unwilling. Simplicity end themselves increasing led day sympathize yet. General windows effects not are drawing man garrets. Common indeed garden you his ladies out yet. Preference imprudence contrasted to remarkably in on. Taken now you him trees tears any. Her object giving end sister except oppose. \r\n\r\nWas justice improve age article between. No projection as up preference reasonably delightful celebrated. Preserved and abilities assurance tolerably breakfast use saw. And painted letters forming far village elderly compact. Her rest west each spot his and you knew. Estate gay wooded depart six far her. Of we be have it lose gate bred. Do separate removing or expenses in. Had covered but evident chapter matters anxious');
When you run a GROUP BY query without using GROUP_CONCAT() result set looks as expected (showing two lines, one for each text option):
SELECT `text` FROM `table` GROUP BY `text`; +
However, when starting the same query with GROUP_CONCAT() result set is not expected (showing one row with a concatenated string of two id fields):
SELECT GROUP_CONCAT(`id` SEPARATOR ', ') AS ids FROM `table` GROUP BY `text`; +
My question is:
Why does using GROUP_CONCAT() affect the number of rows returned?
My initial assumption was that GROUP_CONCAT_MAX_LEN has something to do with it (my value is 1024), but it certainly only affects GROUP_CONCAT() , not GROUP BY (as you can see, I use GROUP_CONCAT() in the id field, and not in the text field, and the result of this is not even close to exceeding GROUP_CONCAT_MAX_LEN ).
mysql select group-by group-concat
MichaelRushton
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