SET [NO]CARDINALITY_CHECK lets you control the WHERE clause singleton subselect cardinality checking.

In previous releases that supported WHERE clause subqueries, a cardinality error (that is, a result contained too many results) was not raised unless SET NOFLATTEN was specified. With the introduction of scalar subqueries, cardinality errors may be reported that were ignored previously.

SET CARDINALITY_CHECK raises the cardinality violation exception and otherwise restores the legacy behavior. The session default setting is derived from a CBF parameter ii.nodename.dbms.*.cardinality_check, which defaults to ON.