Subject Re: [firebird-support] Re: UPDATE AND DELETE WITH JOIN
Author Ann W. Harrison
A problem with the

UPDATE <table> ... FROM <query expression> ...

syntax is that it's not deterministic in general. You
can't predict what the results will be when there is more
than one match for a particular updated row. That
situation raises an error in the standard syntax because
the select in the assignment must return a single value.
I think the ambiguity is the reason the standards committee
rejected the statement.