fix: BigQuery TIMESTAMP and TIMESTAMPTZ types (#1511)

BigQuery does not have a `TIMESTAMPTZ` type. A timestamp with
time zone maps to the [`TIMESTAMP`](https://cloud.google.com/bigquery/docs/reference/standard-sql/data-types#timestamp_type) type and one without a
timezone maps to [`DATETIME`](https://cloud.google.com/bigquery/docs/reference/standard-sql/data-types#datetime_type).

sqlglot/dialects/bigquery.py

@@ -269,6 +269,8 @@ class Generator(generator.Generator):
             exp.DataType.Type.NVARCHAR: "STRING",
             exp.DataType.Type.SMALLINT: "INT64",
             exp.DataType.Type.TEXT: "STRING",
+            exp.DataType.Type.TIMESTAMP: "DATETIME",
+            exp.DataType.Type.TIMESTAMPTZ: "TIMESTAMP",
             exp.DataType.Type.TINYINT: "INT64",
             exp.DataType.Type.VARCHAR: "STRING",
             exp.DataType.Type.VARIANT: "ANY TYPE",

tests/dialects/test_bigquery.py

@@ -22,6 +22,8 @@ def test_bigquery(self):
         self.validate_all("CAST(x AS CHAR)", write={"bigquery": "CAST(x AS STRING)"})
         self.validate_all("CAST(x AS NCHAR)", write={"bigquery": "CAST(x AS STRING)"})
         self.validate_all("CAST(x AS NVARCHAR)", write={"bigquery": "CAST(x AS STRING)"})
+        self.validate_all("CAST(x AS TIMESTAMP)", write={"bigquery": "CAST(x AS DATETIME)"})
+        self.validate_all("CAST(x AS TIMESTAMPTZ)", write={"bigquery": "CAST(x AS TIMESTAMP)"})
         self.validate_all(
             "SELECT ARRAY(SELECT AS STRUCT 1 a, 2 b)",
             write={

tests/dialects/test_duckdb.py

@@ -80,7 +80,7 @@ def test_time(self):
                 "snowflake": "CONVERT_TIMEZONE('America/New_York', CAST(start AS TIMESTAMPTZ))",
             },
             write={
-                "bigquery": "TIMESTAMP(DATETIME(CAST(start AS TIMESTAMPTZ), 'America/New_York'))",
+                "bigquery": "TIMESTAMP(DATETIME(CAST(start AS TIMESTAMP), 'America/New_York'))",
                 "duckdb": "CAST(start AS TIMESTAMPTZ) AT TIME ZONE 'America/New_York'",
                 "snowflake": "CONVERT_TIMEZONE('America/New_York', CAST(start AS TIMESTAMPTZ))",
             },

tests/dialects/test_presto.py

@@ -60,7 +60,7 @@ def test_cast(self):
         self.validate_all(
             "CAST(x AS TIMESTAMP(9) WITH TIME ZONE)",
             write={
-                "bigquery": "CAST(x AS TIMESTAMPTZ)",
+                "bigquery": "CAST(x AS TIMESTAMP)",
                 "duckdb": "CAST(x AS TIMESTAMPTZ(9))",
                 "presto": "CAST(x AS TIMESTAMP(9) WITH TIME ZONE)",
                 "hive": "CAST(x AS TIMESTAMP)",