The Definitive Guide to Data Quality
Use an SQL query on your tInputDB.
..but how can I do the same thing with a left outer join?
My best advice is to use the tELTOracleInput for every tables, a tELTOracleMap to perform your JOIN and transformation via Oracle database then a tELTOracleOutput to store result of the ELT transformation.
ELT transformation generates a SQL query to perform operations and transformation, it's easy to design and very fast and efficient.