Обсуждение: boolean over char(1)

Is there any advantages of using datatype boolean over char(1)? If there
isn't I think char(1) is more portable across other DBM?

"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

Also, we do support "char", which is one byte.  You need to specify the
quotes when creating the column.

---------------------------------------------------------------------------

Tom Lane wrote:
> "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
>
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Bruce Momjian <pgman@candle.pha.pa.us> writes:
> Also, we do support "char", which is one byte.  You need to specify the
> quotes when creating the column.

But he's looking for "more standard", which "char" surely is not.

            regards, tom lane