The AS Clause
Without the AS clause, the user who executes the REVOKE statement must be the grantor of the privilege that is being revoked. The DBA or the owner of the object can use the AS clause to specify another user (who must be the grantor of the privilege) as the revoker of the privileges.
For example, if user falstaff is the owner of table CONS_table, and has granted
The AS clause provides the only mechanism by which discretionary access privileges can be revoked on a database object whose owner is an authorization identifier, such as informix, that is not also a valid user account known to the operating system.
For contexts where the AS revoker clause is required, rather than optional, see Revoking the Execute privilege from PUBLIC.