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# Check the bits of a numeric field

Is it possible to check the bits of a numeric field in the WHERE condition of a SQL request? The only means that...

I found, for example if I want to test the bit 0, is:

```SELECT * FROM MyTable
WHERE NumField IN (1, 3, 5,...)```

Is there another solution?

Yes, what you could do is convert the number to a string representation of its binary value.

In MySQL, there's a very handy function called CONV that will do this:

```create table numbers ( numfield integer );

insert into numbers (numfield) values (0);
insert into numbers (numfield) values (1);
insert into numbers (numfield) values (2);
insert into numbers (numfield) values (3);
insert into numbers (numfield) values (937);
insert into numbers (numfield) values (1234567);

select numfield
, conv(numfield,10,2) as bitstr
from numbers

numfield  bitstr
0  0
1  1
2  10
3  11
937  1110101001
1234567  100101101011010000111```

Now all that's left to do is decide which bit position you want to test. If it's the right-most position, you can use the RIGHT function:

```select numfield
, conv(numfield,10,2) as bitstr
from numbers
where right(conv(numfield,10,2),1) = '0'

numfield  bitstr
0  0
2  10 ```

However, if it's any other position, you will have to figure out the position by using the LENGTH function and counting backwards. Complicating this is the fact that the string might be shorter than you expect, so you'll have to concatenate enough zeroes on to the front of it. For example, to test whether the bit in the eighth position from the right is on, you have start at the end, which is given by the LENGTH function, and them move over 7 positions to the left:

```select numfield
, conv(numfield,10,2) as bitstr
from numbers
where mid('0000000'+conv(numfield,10,2)
,length('0000000'+conv(numfield,10,2))-7
,1) = '1'

numfield  bitstr
937  1110101001
1234567  100101101011010000111```

Other database systems may not have conversion functions exactly like MySQL's CONV. Look for CAST or CONVERT, and check the documentation to see whether you can convert numeric to binary and then binary to character string.

One final note: if you are indeed checking the rightmost bit position, as in your example, then you could also just divide by 2 and see if there's a remainder:

```select numfield
from numbers
where mod(numfield,2) = 1

numfield
1
3
937
1234567```

This was last published in November 2002

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