Permissions: _count operator in permissions?

[petegriffith]

When setting custom permissions, is there a way to use something like _count to check the number of entries on a table?

For instance, a given user role has permission to delete an entry from the special_user table if they are in the special_user table AND there is at least one other special_user in the table. The first half is simple:
{"special_users":{"account":{"auth_uid":{"_eq":"X-Hasura-User-Id"}}}}

But what would the second half of the _and look like? Something like this?
{"special_users":{_COUNT:{"_gt": 0}}

[adas98012]

@petegriffith
One alternative would be to use a computed field that holds the count (returned by a custom sql function), which you can then use in the permissions logic.