Add multiply_full_scale function.

udfs/community/multiply_full_scale.sql

@@ -0,0 +1,28 @@
+/*
+ * Copyright 2019 Google LLC
+ *
+ * Licensed 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.
+ */
+
+/*
+ * BigQuery supports a maximum precision / scale of (38,9) for NUMERIC. For some
+ * applications (e.g financial) it may be necessary to multiply a high scale
+ * number such as an FX Rate against another NUMERIC value. This function takes
+ * in a STRING high_scale_value and multiplies against a multiplier to allow for
+ * high scale multiplication while returning BigQuery's NUMERIC default of (38,9)
+ */
+CREATE OR REPLACE FUNCTION fn.multiply_full_scale(high_scale_value STRING, multiplier NUMERIC) AS (
+  CAST(SPLIT(high_scale_value, '.')[OFFSET(0)] AS NUMERIC) * multiplier +
+  IFNULL(CAST(SPLIT(high_scale_value, '.')[SAFE_OFFSET(1)] AS NUMERIC) * multiplier /
+    POW(NUMERIC '10', LENGTH(SPLIT(high_scale_value, '.')[SAFE_OFFSET(1)])), 0)
+);