Have where clause instead of nvl for null last_altered

Signed-off-by: Zack Wu <[email protected]>

databuilder/extractor/snowflake_table_last_updated_extractor.py

@@ -29,7 +29,7 @@ class SnowflakeTableLastUpdatedExtractor(Extractor):
             lower({cluster_source}) AS cluster,
             lower(t.table_schema) AS schema,
             lower(t.table_name) AS table_name,
-            NVL(DATE_PART(EPOCH, t.last_altered), 0) AS last_updated_time
+            DATE_PART(EPOCH, t.last_altered) AS last_updated_time
         FROM
             {database}.INFORMATION_SCHEMA.TABLES t
         {where_clause_suffix};
@@ -48,7 +48,7 @@ class SnowflakeTableLastUpdatedExtractor(Extractor):
     DEFAULT_CLUSTER_NAME = 'master'
 
     DEFAULT_CONFIG = ConfigFactory.from_dict(
-        {WHERE_CLAUSE_SUFFIX_KEY: ' ',
+        {WHERE_CLAUSE_SUFFIX_KEY: ' WHERE t.last_altered IS NOT NULL ',
          CLUSTER_KEY: DEFAULT_CLUSTER_NAME,
          USE_CATALOG_AS_CLUSTER_NAME: True,
          DATABASE_KEY: 'snowflake',