One of the important prerequisites for querying from metrics table using Oracle SQLDeveloper is to wrap the identifiers within 'Double Quotes" for Oracle to treat with case sensitivity.  In general, double quotes are not needed around an identifier while querying the table in TIBCO Data Virtualization's Studio and many of the other client tools since this is done implicitly. 

When the Execute DDL button is clicked to create and bind the metrics tables, TDV passes the table name/column name within double quotes in the query. When the table (or a column) is created with double quotes around the name, the identifier must be put between the double quotes and should be in proper case i.e. lower case/upper case. So now if the database needs to be accessed then the table name/column name should be put under double-quotes. 

E.g. "table_name", "column_name", etc.

To get rid of the double quotes around table name/column name it is advised to pre-create the external database and tables for metrics data storage rather than creating the tables using Execute DDL. To do so kindly refer to the topic "Pre-Creating the External Database and Tables for Metrics Data Storage" from the TIBCO Data Virtualization's Administration guide present at the path <TDV_Install_Dir>/docs. The guide has information regarding what query needs to be passed to the database in order to create the metric tables.