fix(mysql): TIMESTAMP -> CAST (#2223)

* fix(mysql): TIMESTAMP -> CAST

* fixup

* move to generator

sqlglot/dialects/presto.py

@@ -362,6 +362,7 @@ class Generator(generator.Generator):
             exp.WithinGroup: transforms.preprocess(
                 [transforms.remove_within_group_for_percentiles]
             ),
+            exp.Timestamp: transforms.preprocess([transforms.timestamp_to_cast]),
         }
 
         def interval_sql(self, expression: exp.Interval) -> str:

sqlglot/expressions.py

@@ -4372,6 +4372,10 @@ class Extract(Func):
     arg_types = {"this": True, "expression": True}
 
 
+class Timestamp(Func):
+    arg_types = {"this": False, "expression": False}
+
+
 class TimestampAdd(Func, TimeUnit):
     arg_types = {"this": True, "expression": True, "unit": False}
 

sqlglot/transforms.py

@@ -327,3 +327,12 @@ def _to_sql(self, expression: exp.Expression) -> str:
         raise ValueError(f"Unsupported expression type {expression.__class__.__name__}.")
 
     return _to_sql
+
+
+def timestamp_to_cast(expression: exp.Expression) -> exp.Expression:
+    if isinstance(expression, exp.Timestamp) and not expression.expression:
+        return exp.cast(
+            expression.this,
+            to=exp.DataType.Type.TIMESTAMP,
+        )
+    return expression

tests/dialects/test_presto.py

@@ -358,6 +358,10 @@ def test_time(self):
             write={"presto": "CAST(x AS TIMESTAMP)"},
             read={"mysql": "CAST(x AS DATETIME)", "clickhouse": "CAST(x AS DATETIME64)"},
         )
+        self.validate_all(
+            "CAST(x AS TIMESTAMP)",
+            read={"mysql": "TIMESTAMP(x)"},
+        )
 
     def test_ddl(self):
         self.validate_all(