MySQL group_concat merge row usage and Problems

Group_concat usage

The rules are as follows:

Group_concat ([distinct] expr [, expr...]
[Order by {unsigned_integer | col_name | expr}
[ASC | DESC] [, col_name...]
[Separator str_val])
Problems with group_concat
If the column to be merged is of the int type, the system prompts [blob-7 B] or [blob-7 bytes]. group_concat (cast (ID as char) is required at this time )) as Id instead of group_concat (ID) as ID. Cast is a conversion function.

2. The length of group_concat is limited. The default value of MySQL is 1024 bytes,

If the length is exceeded, I think the data is incomplete. If you are interested, try it. To increase the value, add the following content to [mysqld] In my. CNF:Group_concat_max_len =
10240

, Just restart MySQL.