In a first record join, the sources are prioritized such that, if a record from a higher priority source compares equally to records from lower priority sources, the record from the highest priority source is processed and the records from the lower priority sources are discarded.
Sources are listed in order of decreasing priority in the join configuration.
Records are never combined. The most common use of this join is for handling incremental feeds. For incremental feeds, history data (previously processed records) is given a lower priority and the latest data feed takes precedence. Records from the latest feed replace records in the history data, and records from the history data are processed only if a corresponding record does not exist in the latest feed.
In this example, records A, C, and D from Source 1 are processed, while their equivalents in Source 2 are discarded. Records B and E are both processed because they have no equivalents.
