Bitwise And Operator

Question

Can someone explain this in simpler terms?

The binary representation of 170 is 0000 0000 1010 1010. The binary representation of 75 is 0000 0000 0100 1011. Performing the bitwise AND operation on these two values produces the binary result 0000 0000 0000 1010, which is decimal 10.

0000 0000 1010 1010
0000 0000 0100 1011
-------------------
0000 0000 0000 1010

This will make will click for me once I know what is being done. I have a basic understanding of binaries and know a few off the top of my head... like 1 represented in binary would be 00000001 and 2 would be 00000010 and 3 would be 00000011 and 4 would be 00000100 and 5 would be 00000101 and 6 would be 00000110. So I understand what is going on when you got up a digit each time.

I also understand what is going on when this sql developer is subtracting, but not something is missing when she uses t-sql code to find her answers.... in regards to what is stated in this link.

http://sqlfool.com/2009/02/bitwise-operations/

Answer 1

Look at the individual binary digits in your example as columns. If there is a 1 in both input rows of a particular column, the output is 1 for that column. Otherwise it is 0.

The AND operator can be used to "mask" values. So if you just want the first four low-order bits of a number, you can AND it with 15, like this:

0010 1101 1110 1100
0000 0000 0000 1111
-------------------
0000 0000 0000 1100  <-- the value of the first four bits in the top number

That's what is happening in the SQL example you linked.

freq_interval is one or more of the following:
1 = Sunday
2 = Monday
4 = Tuesday
8 = Wednesday
16 = Thursday
32 = Friday
64 = Saturday

Corresponds to the bit masks:

0000 0001 = Sunday
0000 0010 = Monday
0000 0100 = Tuesday
0000 1000 = Wednesday
0001 0000 = Thursday
0010 0000 = Friday
0100 0000 = Saturday