问题
I am using a group_concat to concatenate a lot of rows into one.
I set group concat to 10000 using:
SET group_concat_max_len = 10000;
But even then, my output cells remain incomplete and end with ...
I tried setting group_concat_max_len = 20000 and even that didn't help.
I also tried setting group_concat_max_len to 99999999. It still doesn't complete my output text. And I checked one of the group concat stops at Length = 230 characters and then gives ...
Is there any other way?
回答1:
Check out this link: https://dev.mysql.com/doc/refman/5.6/en/server-system-variables.html#sysvar_group_concat_max_len
All the MySQL configuration variables are documented on that page, with details like minimum, maximum, default value, whether you can set them globally or per-session, whether you can change them on a running instance or does it require a restart, and other description of usage.
The maximum value for group_concat_max_len is 18446744073709551615.
The group-concat string does not end with "..." If you try to group too much text, it just gets truncated. So I wonder if the problem is not with MySQL's settings, but with the display of your cells.
回答2:
For 32bit systems, the maximum value is 4294967295
For 64 bit systems, the maximum value is 18446744073709551615.
You can set the variable for your current session using
SET SESSION group_concat_max_len=4294967295;
To set the variable forever use
SET GLOBAL group_concat_max_len=4294967295;
(see http://dev.mysql.com/doc/refman/5.7/en/server-system-variables.html#sysvar_group_concat_max_len)
来源：https://stackoverflow.com/questions/26553823/what-is-the-maximum-allowance-for-group-concat-max-len-in-mysql