Grammar: Add DROP POLICY statement to postgres dialect (#2024)

src/sqlfluff/dialects/dialect_postgres.py

@@ -2182,6 +2182,7 @@ class StatementSegment(BaseSegment):
             Ref("SetStatementSegment"),
             Ref("DropFunctionStatementSegment"),
             Ref("CreatePolicyStatementSegment"),
+            Ref("DropPolicyStatementSegment"),
         ],
     )
 
@@ -2452,3 +2453,23 @@ class CreatePolicyStatementSegment(BaseSegment):
         Sequence("USING", Bracketed(Ref("ExpressionSegment")), optional=True),
         Sequence("WITH", "CHECK", Bracketed(Ref("ExpressionSegment")), optional=True),
     )
+
+
+@postgres_dialect.segment()
+class DropPolicyStatementSegment(BaseSegment):
+    """A `DROP POLICY` statement.
+
+    As Specified in https://www.postgresql.org/docs/14/sql-droppolicy.html
+    """
+
+    type = "drop_policy_statement"
+    match_grammar = StartsWith(Sequence("DROP", "POLICY"))
+    parse_grammar = Sequence(
+        "DROP",
+        "POLICY",
+        Ref("IfExistsGrammar", optional=True),
+        Ref("ObjectReferenceSegment"),
+        "ON",
+        Ref("TableReferenceSegment"),
+        OneOf("CASCADE", "RESTRICT", optional=True),
+    )

test/fixtures/dialects/postgres/postgres_drop_policy.sql

@@ -0,0 +1,5 @@
+DROP POLICY account_managers ON accounts;
+DROP POLICY IF EXISTS account_managers ON accounts;
+DROP POLICY account_managers ON accounts CASCADE;
+DROP POLICY account_managers ON accounts RESTRICT;
+DROP POLICY IF EXISTS account_managers ON accounts RESTRICT;

test/fixtures/dialects/postgres/postgres_drop_policy.yml

@@ -0,0 +1,64 @@
+# YML test files are auto-generated from SQL files and should not be edited by
+# hand. To help enforce this, the "hash" field in the file must match a hash
+# computed by SQLFluff when running the tests. Please run
+# `python test/generate_parse_fixture_yml.py`  to generate them after adding or
+# altering SQL files.
+_hash: 5e9709e8abf96cd4c55171f63ddb5b2dbc1c2b9298c8d6ff94ac36e11a7675ef
+file:
+- statement:
+    drop_policy_statement:
+    - keyword: DROP
+    - keyword: POLICY
+    - object_reference:
+        identifier: account_managers
+    - keyword: 'ON'
+    - table_reference:
+        identifier: accounts
+- statement_terminator: ;
+- statement:
+    drop_policy_statement:
+    - keyword: DROP
+    - keyword: POLICY
+    - keyword: IF
+    - keyword: EXISTS
+    - object_reference:
+        identifier: account_managers
+    - keyword: 'ON'
+    - table_reference:
+        identifier: accounts
+- statement_terminator: ;
+- statement:
+    drop_policy_statement:
+    - keyword: DROP
+    - keyword: POLICY
+    - object_reference:
+        identifier: account_managers
+    - keyword: 'ON'
+    - table_reference:
+        identifier: accounts
+    - keyword: CASCADE
+- statement_terminator: ;
+- statement:
+    drop_policy_statement:
+    - keyword: DROP
+    - keyword: POLICY
+    - object_reference:
+        identifier: account_managers
+    - keyword: 'ON'
+    - table_reference:
+        identifier: accounts
+    - keyword: RESTRICT
+- statement_terminator: ;
+- statement:
+    drop_policy_statement:
+    - keyword: DROP
+    - keyword: POLICY
+    - keyword: IF
+    - keyword: EXISTS
+    - object_reference:
+        identifier: account_managers
+    - keyword: 'ON'
+    - table_reference:
+        identifier: accounts
+    - keyword: RESTRICT
+- statement_terminator: ;