I propose to add a new value "no_data_found" for the plpgsql.extra_errors and plpgsql.extra_warnings parameters [1].
With plpgsql.extra_errors=no_data_found SELECT INTO raises no_data_found exception when the result set is empty. With plpgsql.extra_errors=too_many_rows,no_data_found SELECT INTO behaves like SELECT INTO STRICT [2]. This could simplify migration from PL/SQL and may be just more convenient.
One potential downside is that plpgsql.extra_errors=no_data_found could break existing functions expecting to get null or checking IF found explicitly. This is also true for the too_many_rows exception, but arguably it's a programmer error, while no_data_found switches to a different convention for handling (or not handling) an empty result with SELECT INTO.
Otherwise the patch is straightforward.
What do you think?
I am not against it. It makes sense.
I don't like the idea about possible replacement of INTO STRICT by INTO + extra warnings.
Handling exceptions is significantly more expensive than in Oracle, and using INTO without STRICT with the next test IF NOT FOUND THEN can save one safepoint and one handling an exception. It should be mentioned in the documentation. Using this very common Oracle's pattern can have a very negative impact on performance in Postgres. If somebody does port from Oracle, and wants compatible behavior then he should use INTO STRICT. I think it is counterproductive to hide syntax differences when there is a significant difference in performance (and will be).
