Unique Constraint with conditions in MYSQL

Question

In postgres we have a constraint defined that essentially allows us to limit the number of entries in a table with a certain value to one. We created this constraint:

Answer 1

My two cents:

why don't you create a column only to store the unique value (maybe you can call it something like is_list_type_default) and another to store all the values. If you do this, you can put a unique constraint on the first column.