Break up db_engine_specs (#7676)

* Refactor db_engine_specs into package

* Rename bigquery class and add epoch funcs

* Fix flake8 errors

* Dynamically load all engine specs

* Fix linting errors and unit tests

* Implement Snowflake epoch time funcs

* Implement Teradata epoch time func

* Fix presto datasource query and remove unused import

* Fix broken datasource query

* Add mypy ignore for false positive

* Add missing license files

* Make create_time_grains_tuple public

* Fix flake8 quote

* Fix incorrect licence header

superset/db_engine_specs/redshift.py

@@ -0,0 +1,32 @@
+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you under the Apache License, Version 2.0 (the
+# "License"); you may not use this file except in compliance
+# with the License.  You may obtain a copy of the License at
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing,
+# software distributed under the License is distributed on an
+# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+# KIND, either express or implied.  See the License for the
+# specific language governing permissions and limitations
+# under the License.
+# pylint: disable=C,R,W
+from superset.db_engine_specs.postgres import PostgresBaseEngineSpec
+
+
+class RedshiftEngineSpec(PostgresBaseEngineSpec):
+    engine = 'redshift'
+    max_column_name_length = 127
+
+    @staticmethod
+    def mutate_label(label):
+        """
+        Redshift only supports lowercase column names and aliases.
+        :param str label: Original label which might include uppercase letters
+        :return: String that is supported by the database
+        """
+        return label.lower()