estimates the distinct number of field values in the join . since the join does not increase or decrease field values , the estimate is the same as in the appropriate underlying query . concode_field_sep String fldname2 concode_elem_sep Plan p1 concode_elem_sep String fldname1 concode_elem_sep Plan p2 concode_elem_sep Schema sch concode_field_sep Schema schema concode_elem_sep int blocksAccessed concode_elem_sep int recordsOutput concode_elem_sep Scan open