Add optional MySQL-style ON UPDATE to columns

[katzyn]

An implementation of feature request #219.

This feature is available in all modes because in may be useful in default mode to.

CREATE TABLE and ALTER TABLE ADD COLUMN syntax is the same as in MySQL.

ALTER TABLE ALTER COLUMN syntax for changing existing columns is not compatible with MySQL, because in MySQL such parameters cannot be changed in regular way, CHANGE should be used instead, but H2 don't have this MySQL extension.

This implementation is not limited to date-time columns and CURRENT_TIMESTAMP function, any column and any expression can be used, just like in DEFAULT.

If update statement does not change any values in a row ON UPDATE column does not change its value, like in MySQL. Explicit value for this column can be specified to prevent execution of ON UPDATE expression also like in MySQL.

Non-standard INFORMATION_SCHEMA.COLUMNS.COLUMN_ON_UPDATE field is introduced. (COLUMN_DEFAULT was already here, so name for ON UPDATE follows this name convention).

Documentation is updated.

Minor issues with building of documentation are also fixed.

[tazmaniax]

@katzyn thanks for making this improvement! Do you have an idea when this might be included in a release?

[katzyn]

It will be included in the next release, but I have no idea when the next release will be built and published.

You can clone current sources or download them here on GitHub and build database for yourself with jar target:
http://www.h2database.com/html/build.html#building
Some additional testing before the release would be nice.

[cpaika]

Really appreciate this improvement! Big help for us