If a field is created with :
fieldname SMALLINT UNSIGNED DEFAULT 0

Then using

GREATEST(0, fieldname-1)

in SELECT or UPDATE
will trigger an error and not give results
ERROR 1690 (22003): BIGINT UNSIGNED value is out of range in '`db`.`table`.`fieldname` - 1'

Actual example for SELECT:

select greatest(1,loc_count-1) from Custom_Lists;
ERROR 1690 (22003): BIGINT UNSIGNED value is out of range in '`pj_dev`.`Custom_Lists`.`loc_count` - 1'

same for UPDATE

The error should only be triggered in a direct field,not using GREATEST()