Handle more SQL types

[paluh]

In SQL1992 we have:

SQL defines distinct data types named by the following <key word>s:
CHARACTER, CHARACTER VARYING, BIT, BIT VARYING, NUMERIC, DECIMAL,
INTEGER, SMALLINT, FLOAT, REAL, DOUBLE PRECISION, DATE, TIME,
TIMESTAMP, and INTERVAL.

For sure we can easily extend and add support for DOUBLE PRECISION (Number). We can also explore datetime related types and check if all interesting db backends handle these values consistently.