Arithmetic on optionals

[dbrgn]

This does not work...

update(posts.filter(id.eq(7)).set(read_count.eq(read_count + 1))

...if read_count is nullable.

According to my tests, Pg, MySQL and SQLite all return null for SELECT NULL + 1.

This page seems to agree: http://www-cs-students.stanford.edu/~wlam/compsci/sqlnulls

An arithmetic operation involving a NULL returns NULL. For example, NULL minus NULL yields NULL, not zero.

I didn't check the SQL ISO standard though.

Note also that aggregation function like SUM() seem to ignore null values.

Maybe addition and other arithmetic operations could be implemented on Nullable<Integer> and others?

[sgrif]

The ISO standard is that any operation on a null value returns null. I'm fine with adding ops for nullable values (preferably as a single blanket impl if possible)