The following items define the meaning of single row with respect to source table rules and limitations for MERGE requests:
The specified match_condition must specify a single primary index for the target row.
If you specify a subquery for source_table_reference, then that subquery must be a singleton SELECT (that is, it cannot retrieve more
than a single row from the referenced table) and it must specify either a UPI or USI
to make the retrieval. The selected columns must be referenced explicitly: the SELECT *
syntax is not permitted.
If you specify a simple list of column values for source_table_reference, then the retrieval, by definition, retrieves only a single row.