What is the maximum allowance for group_concat_max_len in MySQL?

Question

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;

Answer 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.

Answer 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)