Feat(postgres): transpile QUARTER interval unit (#5015)

Author: georgesittas

sqlglot/dialects/postgres.py

@@ -742,3 +742,12 @@ def isascii_sql(self, expression: exp.IsAscii) -> str:
         @unsupported_args("this")
         def currentschema_sql(self, expression: exp.CurrentSchema) -> str:
             return "CURRENT_SCHEMA"
+
+        def interval_sql(self, expression: exp.Interval) -> str:
+            unit = expression.text("unit").lower()
+
+            if unit.startswith("quarter") and isinstance(expression.this, exp.Literal):
+                expression.this.replace(exp.Literal.number(int(expression.this.to_py()) * 3))
+                expression.args["unit"].replace(exp.var("MONTH"))
+
+            return super().interval_sql(expression)

tests/dialects/test_postgres.py

@@ -372,6 +372,14 @@ def test_postgres(self):
             pretty=True,
         )
 
+        self.validate_all(
+            "SELECT CURRENT_TIMESTAMP + INTERVAL '-3 MONTH'",
+            read={
+                "mysql": "SELECT DATE_ADD(CURRENT_TIMESTAMP, INTERVAL -1 QUARTER)",
+                "postgres": "SELECT CURRENT_TIMESTAMP + INTERVAL '-3 MONTH'",
+                "tsql": "SELECT DATEADD(QUARTER, -1, GETDATE())",
+            },
+        )
         self.validate_all(
             "SELECT ARRAY[]::INT[] AS foo",
             write={