Bug #65651 SET improvement
Submitted: 18 Jun 2012 10:52 Modified: 29 Jun 2012 6:39
Reporter: Angel Tsvetkov Email Updates:
Status: Verified Impact on me:
Category:MySQL Server: Data Types Severity:S5 (Performance)
Version: OS:Any
Assigned to: CPU Architecture:Any
Tags: SET

[18 Jun 2012 10:52] Angel Tsvetkov
How can increase limitation of 64 max members of SET?
(A SET can have a maximum of 64 different members.)

How to repeat:
How can increase limitation of 64 max members of SET?
(A SET can have a maximum of 64 different members.)
[18 Jun 2012 13:01] Valeriy Kravchuk
There is no way to do this currently. Probably entirely new implementation for SET data type will be needed in this case. 

What maximum number of different elements would you like to see supported?
[27 Jun 2012 10:36] Joachim Jellinek
I would also like this limit to be flexible / increased (having just reached it on a system coded 14 years ago with a lot of code written by someone else, but relying heavily on a number of sets!)

What are the reasons for the current 64 limit, could it be increased by configuration? Why have a limitation at all?
[29 Jun 2012 6:39] Valeriy Kravchuk
Probably current limit has something to do with 8 byte numbers and bit operations used. 

In any case, this is a reasonable feature request for a new implementation to support sets with more items.
[18 Jul 2012 18:30] Trey Raymond
Binary bitmaps in mysql currently can go up to 1024 members, using a BINARY(128) field, and a function like:
insert into table_with_bitmap
select $other_field_values,unhex(hex(sum(pow(2,id))))
from item_dimension
where item_name in ('item1','item3','item7');

However actually using the data like that is sloppy.  With the mathematical limit of mysql being <2^1024, SET type could feasibly store up to 1024 unique values with some changes to how it's stored.  It already uses variable length (up to 8 bytes) using behind the scenes numeric types to store (tinyint-bigint), but stored as binary data it could be byte by byte variable from 1B to 128B.

One possible requirement, however, would be to eliminate the 64b math limitation on bitwise operations, assuming that is the same math used behind the scenes when mysql stores set fields.