1. A method comprising: executing a plurality of transform stages in an extract, transform and load (ETL) job, the ETL job including an extract stage and a load stage in addition to the plurality of transform stages, and the ETL job configured to access a source database table that includes data organized into source database table rows and source database table columns, the executing comprising for each transform stage: receiving, from an upstream stage, a plurality of input row identifiers (RIDs) corresponding to a first plurality of source database table rows in the source database table; retrieving data directly from a subset of the source database table columns in the first plurality of source database table rows in the source database table, the retrieving responsive to the input RIDs and to transform logic associated with the transform stage; generating partial row data for each of the first plurality of source database table rows, the partial row data comprising data from the subset of the source database table columns; generating transformed data responsive to the partial row data and to the transform logic; and outputting, to a downstream stage, a plurality of output RIDs corresponding to a second plurality of source database table rows that include at least a subset of the transformed data.