Exclude one table from another

To find all records in t0 that are not in t1, you should perform the following steps:
  • Create a transform on t0
  • Create a left join t1 on t0 with your join condition(s)
    • E.g., left join t1 where t0.patid = t1.patid
  • Create a new row filter, removing all records where a column (which you know to be non-null) in t1 is non-null in the join
    • E.g., filter records where t1.patid != NULL , given that t1.patid is never NULL in t1
  • This selects all records in t0 where the join didn't find any matches in t1; that is, the set of all records that are in t0 but not in t1.