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.