Re: bit operations

On Wed, Jul 04, 2001 at 02:56:06PM +0100, Richard Huxton wrote:
> From: "Johan Björk" <johan@websidorna.com>
>
> > Have a little problem with bit operaitions that I cannot find the answer
> to on the Internet. Have been searching through the archives but no result.
> >
> > In MySQL you can have a INT column and do bit logic ala C-style like this:
> > "select * from table where flags & 4;"
>
> If you're using an int for "flags":
>
> select * from table where (flags & 4) > 0;
>
> The bitwise AND returns an integer rather than a boolean, and AFAIK SQL
> doesn't follow C's rules on this.
>
> > Can I do something similar with std SQL? I've been trying to cast
> everything to BIT but without success, and I've also been creating a "flags
> bit(4)", setting a row to "1000" (8) and trying to compare, but I have
> absolutely no idea how to.
> >
> > Say I wanna check if 8 (1xxx) and 2 (xx1x) is set, how do I do that?!
>
> To check two values just do:
>
>   SELECT * FROM table WHERE (flags & val1 & val2) > 0;

i don't think so.

    val1 := 8 := 01000
    val2 := 2 := 00010
    val1 & val2  00000 zero

probably you meant

    (flags & val1) > 0 and (flags & val2) > 0
or
    flags & (val1 + val2) > 0

> If you want to use BIT types you'll need something like:
>
>   SELECT * FROM table WHERE (flags & '0010100'::BIT) <> '0'::BIT;
>
> and updates like
>
>   UPDATE table SET flags = flags | '0001000'::BIT;
>
> Note the need to have the same string-length when using AND/OR.

cool. thanks.

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