These were not in the original PR, so I added them.

All of these except cascade are identical to GRANT, right? I wonder whether we could abstract them a way in a new node such as:

class DCL(Expression):
  arg_types = {
    ...
  }

class Grant(DCL):
  pass

class Revoke(DCL):
 pass

You could extract the dictionary itself out instead of introducing a new common node, perhaps? Until a need arises for it, like DDL etc.

Ditto about these tests, could we merge them such as:

dcl_cmds = [
"SELECT ON TABLE users TO role1",
 ...
]
    
for sql in dcl_cmds:
 with self.subTest(f"Testing PostgreSQL's GRANT statement: {sql}"):
    self.validate_identity(f"GRANT {sql}")

 with self.subTest(f"Testing PostgreSQL's REVOKE statement: {sql}"):
    self.validate_identity(f"REVOKE {sql}")

I did a round a refactoring on these basically doing string substitution for TO & FROM, then I realized it made the tests much harder to read. Yes, it did DRY up the tests a bit. But, I think for testing, it's much better to see the test cases exactly as they are instead of having to trace through the code just to see what the test cases are. So, a little bit of duplications is probably ok here.

@VaggelisD @georgesittas what do you think? If you guys really want to keep these test cases DRY, I can finish the refactoring.

I'm good either way. Happy to just get this in to unblock you.