"Thomas T. Thai" <tom@minnesota.com> writes:
> Is there any advantages of using datatype boolean over char(1)?
boolean fits in 1 byte; char(1) requires 5 bytes (maybe more, depending
on alignment considerations).
boolean will be considerably faster to operate on, being pass-by-value.
char(1) will happily accept values that don't correspond to booleans
(eg, if you use 't' and 'f' to represent booleans in a char(1), what
will you do with 'y' or 'z'?) You could possibly fix that with a
check constraint, but that slows things down still more.
boolean is, um, boolean: it behaves as expected in boolean expressions.
You can't do AND, OR, NOT directly on chars.
> If there isn't I think char(1) is more portable across other DBM?
The boolean datatype is standard in SQL99.
regards, tom lane