Thread: Comparing bit in an integer field

Hello

I need to compare the bit values of a integer field in my table. For example, I have a table called "t1" with just one field "a1" having following values:

a1
==
0
12
8
0
1
10
7
19

I am trying to fetch all records where the 3rd binary bit is 1, which from the above example should be 12 (00001100) and 7 (00000111). If I convert the values to binary and store it as string, I can easily compare them using substr, but would rather like to retain the integer field. I have tried using the get_bit function, but it seems my understanding of the function is not correct.

I would appreciate any help in this regard.


Amitabh

2009/11/16 Amitabh Kant <amitabhkant@gmail.com>:
> Hello
>
> I need to compare the bit values of a integer field in my table. For
> example, I have a table called "t1" with just one field "a1" having
> following values:
>
> a1
> ==
> 0
> 12
> 8
> 0
> 1
> 10
> 7
> 19
>
> I am trying to fetch all records where the 3rd binary bit is 1, which from
> the above example should be 12 (00001100) and 7 (00000111). If I convert the
> values to binary and store it as string, I can easily compare them using
> substr, but would rather like to retain the integer field. I have tried
> using the get_bit function, but it seems my understanding of the function is
> not correct.
>
> I would appreciate any help in this regard.
>
>
> Amitabh
>

There's probably a clean way of doing this, but you could do:

SELECT a1
FROM t1
WHERE (a1::bit(10) & 4::bit(10))::int = 4;

 a1
----
 12
  7
(2 rows)

Regards

Thom

In response to Amitabh Kant :
> Hello
>
> I need to compare the bit values of a integer field in my table. For example, I
> have a table called "t1" with just one field "a1" having following values:
>
> a1
> ==
> 0
> 12
> 8
> 0
> 1
> 10
> 7
> 19
>
> I am trying to fetch all records where the 3rd binary bit is 1, which from the
> above example should be 12 (00001100) and 7 (00000111). If I convert the values
> to binary and store it as string, I can easily compare them using substr, but
> would rather like to retain the integer field. I have tried using the get_bit
> function, but it seems my understanding of the function is not correct.

test=# select * from t1;
 a1
----
  0
 12
  8
  0
  1
 10
  7
 19
(8 rows)

test=*# select a1 from t1 where (a1>>2)::bit = B'1';
 a1
----
 12
  7
(2 rows)


Regards, Andreas
--
Andreas Kretschmer
Kontakt:  Heynitz: 035242/47150,   D1: 0160/7141639 (mehr: -> Header)
GnuPG: 0x31720C99, 1006 CCB4 A326 1D42 6431  2EB0 389D 1DC2 3172 0C99

2009/11/16 A. Kretschmer <andreas.kretschmer@schollglas.com>:
> In response to Amitabh Kant :
>> Hello
>>
>> I need to compare the bit values of a integer field in my table. For example, I
>> have a table called "t1" with just one field "a1" having following values:
>>
>> a1
>> ==
>> 0
>> 12
>> 8
>> 0
>> 1
>> 10
>> 7
>> 19
>>
>> I am trying to fetch all records where the 3rd binary bit is 1, which from the
>> above example should be 12 (00001100) and 7 (00000111). If I convert the values
>> to binary and store it as string, I can easily compare them using substr, but
>> would rather like to retain the integer field. I have tried using the get_bit
>> function, but it seems my understanding of the function is not correct.
>
> test=# select * from t1;
>  a1
> ----
>  0
>  12
>  8
>  0
>  1
>  10
>  7
>  19
> (8 rows)
>
> test=*# select a1 from t1 where (a1>>2)::bit = B'1';
>  a1
> ----
>  12
>  7
> (2 rows)
>

Ah, bit-shifting.  Told you there'd be a cleaner way ;)

Thanks. That should solve my problem.

Amitabh