Aggregate, AggregateFunction, Trigger, and TriggerAdapter

[katzyn]

These interfaces have some problems.

1. Values are converted to Java objects and some conversions are slow, buggy and may loss some information. TIME, DATE, and TIMESTAMP are especially affected, because default JDBC mapping use unreliable legacy datetime data types. I don't know what to do here. Value is not a part of API and this class and its subclasses are modified very often. JSR-310 data types can be used, but they also may loss some information, because H2 has a wider range of values to support the Instant data type properly.

2. Data type information should use implementations of java.sql.SQLType instead of integer codes, because constants from Types don't cover types that aren't included into JDBC specification (even some data types from the SQL Standard aren't included), and Aggregate uses internal codes that are going to be changed. But we need to implement Add own enumeration of data types to API #2194 first.

3. Aggregate and AggregateFunction aren't suitable for external on-disk results.

[grandinj]

Note that none of these things is performance critical, nor are they typically used for extremely large result sets.

They are designed for simplicity, easy of use, and familiarity, so that people can implement their own custom tweaks to various things.

I'd hate to lose that when no-one is complaining about issues with these features.

[katzyn]

I don't care about their performance, but they definitely have bugs with datetime data types and their usability is questionable.

On the other hand, I have a pure SQL triggers and functions in my to-do list.