MySQL bitwise operations

Question

I am trying to understand bitwise operators in MySQL.

I have:

SELECT 1 & 51 FROM bits = 1
SELECT 2 & 51 FROM bits = 2
SELECT 3 & 51 FROM bits = 3
SELECT 4 & 51 FROM bits = 0
SELECT 5 & 51 FROM bits = 1
SELECT 6 & 51 FROM bits = 2

With SELECT 1 & 51 FROM bits is this asking that the first bit (1) is present in both 1 and 51, if it is then I understand this.

But SELECT 6 & 51 FROM bits = 2 doesn't make sense to me as the 6th bit would be 32(?) which isn't is 6, as 6 is made from the 2nd and 4th bit(?), but 32 is present in 51.

So I am a bit confused as to how this works, could someone please explain?

Mureinik · Accepted Answer · 2015-10-12 12:13:21Z

1

The two arguments aren't the indexes of the bits - it means you represent each number in binary, and perform the operation between each bit independently.

 6 in binary: 000110
51 in binary: 110011
AND           ======
              000010

The result, 000010, is the binary representation of 2.

(Note the the preceeding zeros were truncated for clarity's sake)

answered Oct 12, 2015 at 12:13

Mureinik

316k54 gold badges402 silver badges406 bronze badges

Sign up to request clarification or add additional context in comments.

10 Comments

imperium2335 Over a year ago

So it's saying that the bit "2" is present in both 6 and 51, even though 4 is not?

Mureinik Over a year ago

Yes. 6=4+2; 51=32+16+2+1

imperium2335 Over a year ago

So 4 & 51 is 0 because 4: 000100 and 51: 110011, and the bit in 4 isn't used in 51?

Mureinik Over a year ago

@imperium2335 yes, exactly.

imperium2335 Over a year ago

So 4 | 51 would return 4 because 000100 is in 4?

|

Gordon Linoff · Accepted Answer · 2015-10-12 12:09:34Z

0

"6" doesn't refer to the sixth bit. It refers to the binary value. With 8 bits: 00000110.

If you want the sixth bit, use either 1<<6 or 32.

answered Oct 12, 2015 at 12:09

Gordon Linoff

1.3m62 gold badges706 silver badges857 bronze badges

2 Comments

imperium2335 Over a year ago

So Mysql goes right to left and not left to right like PHP?

Gordon Linoff Over a year ago

@imperium2335 . . . The documentation describes "1 << 2" as 4. I don't know how PHP defines this construct, but this does but the low-order bits on the right.

Collectives™ on Stack Overflow

MySQL bitwise operations

2 Answers 2

10 Comments

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

10 Comments

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related