TBOOLEAN class looks like logical type but works differently

[danchanka]

Right now, the TBOOLEAN class looks like a normal logical type, but it works in a different way:

• Both TTRUE and TFALSE are treated as TRUE in logical expressions. This is not what most people expect.
• The name TBOOLEAN sounds like a regular logical type, but it is not.

Suggestion:

Maybe use a different name for the class, like STATE or TRISTATE, or something similar. Also, the literals could have more clear names, like YES/NO/NULL for example.

Or, if the names stay the same, we should explain clearly in the documentation that this class is not a logical type.