mysql & group_concat_length

Let say I have a table with million of rows.

Does this sql query stop as soon as "group_concat_length" limit value is reached for all "id_list" or does it test all rows in the table?

SELECT GROUP_CO开发者_JS百科NCAT(id) AS id_list, type FROM table WHERE 1 GROUP BY type

All rows and groups are processed

Only an individual aggregation is truncated

http://dev.mysql.com/doc/refman/5.5/en/server-system-variables.html