>>You can create a domain that can emulate a logical column.
>>

>>CREATE DOMAIN LOGICAL AS SMALLINT DEFAULT 0 CHECK (VALUE IN (0,1))
>>

>
>This means that we can create custom datatypes or atleast custom datatype names?
>

Hi
Yes, you can. If you have columns with similar characteristics or check constraints, you can create a domain and use it for columns definitions in all tables where you need it.

>>If you are using domains for columns definition, you can easily change all columns based on a certain domain in all tables.
>
>I just go in for the defaults.
>
>>The good news are that records are not physically changed untill they are "visited"
>
>In what manner

Suppose that you have a domain defined as NUMERIC(12,3) used in many tables, some of them with millions of records. If you change the domain to NUMERIC(15,3), this doesn't mean a long running task that implies changes in all tables. Instead, the engine is smart enough to do conversions only when a record with changed column definition is visited/changed in a read/write operation.