Re: Why does a group_concat on a join change aggregate values?
On 2015/05/07 19:42, Paul Halliday wrote: Should have showed the whole thing. Take a look here (click image to see full output): http://www.pintumbler.org/tmp I don't see why this worries you. Joining often increases variation. Indeed, if in some case an inner join never did, maybe the joined tables are needlessly separate. -- MySQL General Mailing List For list archives: http://lists.mysql.com/mysql To unsubscribe:http://lists.mysql.com/mysql
Re: Why does a group_concat on a join change aggregate values?
Hi Paul, On 5/7/2015 10:17 AM, Paul Halliday wrote: Fighting a bit with this one... If I do something like (pseudo): SELECT count(val) AS n, GROUP_CONCAT(types) AS c_types FROM tbl1 returns something like: n c_types 1 t9 when I add a left join though: SELECT count(val) AS n, GROUP_CONCAT(types) AS c_types, GROUP_CONCAT(two.types) AS d_types FROM tbl1 LEFT JOIN tbl2 AS two ON tbl1.id = tbl2.id returns something like: val c_types d_types 3t9,t9,t9 a2,a3,a9 I can have as many group_concats against the same table with varying results and they don't affect COUNT() but once I do that JOIN things start to fall apart. What is happening behind the scenes? Thanks! Here's a simple test. Change the query to no longer have the aggregate functions, then start counting rows by hand. SELECT val AS n , types AS c_types , two.types AS d_types FROM tbl1 LEFT JOIN tbl2 AS two ON tbl1.id = tbl2.id The other thing that springs to mind is that you lack a GROUP BY in your query. It isn't required but they can often help get you to the correct answer. Best regards, -- Shawn Green MySQL Senior Principal Technical Support Engineer Oracle USA, Inc. - Hardware and Software, Engineered to Work Together. Office: Blountville, TN -- MySQL General Mailing List For list archives: http://lists.mysql.com/mysql To unsubscribe:http://lists.mysql.com/mysql
Re: Why does a group_concat on a join change aggregate values?
Should have showed the whole thing. Take a look here (click image to see full output): http://www.pintumbler.org/tmp On Thu, May 7, 2015 at 4:11 PM, shawn l.green shawn.l.gr...@oracle.com wrote: Hi Paul, On 5/7/2015 10:17 AM, Paul Halliday wrote: Fighting a bit with this one... If I do something like (pseudo): SELECT count(val) AS n, GROUP_CONCAT(types) AS c_types FROM tbl1 returns something like: n c_types 1 t9 when I add a left join though: SELECT count(val) AS n, GROUP_CONCAT(types) AS c_types, GROUP_CONCAT(two.types) AS d_types FROM tbl1 LEFT JOIN tbl2 AS two ON tbl1.id = tbl2.id returns something like: val c_types d_types 3t9,t9,t9 a2,a3,a9 I can have as many group_concats against the same table with varying results and they don't affect COUNT() but once I do that JOIN things start to fall apart. What is happening behind the scenes? Thanks! Here's a simple test. Change the query to no longer have the aggregate functions, then start counting rows by hand. SELECT val AS n , types AS c_types , two.types AS d_types FROM tbl1 LEFT JOIN tbl2 AS two ON tbl1.id = tbl2.id The other thing that springs to mind is that you lack a GROUP BY in your query. It isn't required but they can often help get you to the correct answer. Best regards, -- Shawn Green MySQL Senior Principal Technical Support Engineer Oracle USA, Inc. - Hardware and Software, Engineered to Work Together. Office: Blountville, TN -- MySQL General Mailing List For list archives: http://lists.mysql.com/mysql To unsubscribe:http://lists.mysql.com/mysql -- Paul Halliday http://www.pintumbler.org/
Why does a group_concat on a join change aggregate values?
Fighting a bit with this one... If I do something like (pseudo): SELECT count(val) AS n, GROUP_CONCAT(types) AS c_types FROM tbl1 returns something like: n c_types 1 t9 when I add a left join though: SELECT count(val) AS n, GROUP_CONCAT(types) AS c_types, GROUP_CONCAT(two.types) AS d_types FROM tbl1 LEFT JOIN tbl2 AS two ON tbl1.id = tbl2.id returns something like: val c_types d_types 3t9,t9,t9 a2,a3,a9 I can have as many group_concats against the same table with varying results and they don't affect COUNT() but once I do that JOIN things start to fall apart. What is happening behind the scenes? Thanks! -- Paul Halliday http://www.pintumbler.org/
