comparing bit array to bit mask in tsql - sql

Question

I've been working with tsql for quite a while now but I've never seen binary anding or oring in WHERE clause. Now I'm developing new application that would benefit from applying a bitmask.
Lets say I have 16 product grades. Each grade is representrd by a bit position in a bit[] column. So grade A109 would be 0000000000000001, grade B704 would be 0000001000000000, grade V64 is 0100000000000000 and so on. Any grade can only have single 1 in its array column. Now let's say I can turn each of those 3 grades into one another in manufacturing process. So my bit mask for this search would be 0100001000000001. How would I write a WHERE clause to list items of all those 3 grades?

Answer 1

I did some more research and the best solution is to compare masks with bitwise AND operator like this
WHERE mask1 & mask2 <> 0
This is easy, simple and cohesive.

Answer 2

First time for me too. Interesting.
declare #A109 int = 1;
declare #B704 int = 512;
declare #V64 int = 16384;
declare #Xx int = 32;
declare #mask int = 16897; --#A109+#B704+#V64
create table #MyData (
name char(2),
value int);
insert #MyData
values ('a', #A109), ('b1', #B704), ('b2',#B704), ('c', #Xx);
select
name,
value
from #MyData
where (value & #mask) in (#A109, #B704, #V64);
drop table #MyData;
It seems you can't do bitwise operations on binary data! "In a bitwise operation, only one expression can be of either binary or varbinary data type".

Answer 3

In your UI allow the user to select as many grades as (s)he likes. Behind the scenes each grade maps to an int - the Grading table from MarkD's solution. Sum these ints in the application. Pass the total to the SP.
SQL:
create procedure dbo.GetMaskedList #mask int = 0;
...
WHERE BinGrading = #mask;
UI:
int mask = 0;
foreach(item in selectList)
{
mask += item.BinScore;
}
exec GetMaskedList #mask = mask;

Answer 4

In this case, the WHERE clause would be quite simple as you would deal with the decimal (base 10) counterparts of the binary numbers... Where it gets cute, is on the JOIN. To clarify, the approach does not use a bit[] column or a BINARY type - just INT.
Hope you find this helpful.
DECLARE #G1 INT = 1, -- 0000001
#G2 INT = 2, -- 0000010
#G3 INT = 4, -- 0000100
#G4 INT = 8, -- 0001000
#G5 INT = 16, -- 0010000
#G6 INT = 32, -- 0100000
#G7 INT = 64 -- 1000000
;WITH Grading (Grade, BinScore) AS
(
SELECT 'G1', 1 UNION ALL
SELECT 'G2', 2 UNION ALL
SELECT 'G3', 4 UNION ALL
SELECT 'G4', 8 UNION ALL
SELECT 'G5', 16 UNION ALL
SELECT 'G6', 32 UNION ALL
SELECT 'G7', 64
)
,Product (ProductName, BinGrading) AS
(
SELECT 'Foobar', 73 UNION ALL
SELECT 'Franglesnap', 3 UNION ALL
SELECT 'Mebble', 32
)
SELECT *
FROM Product
WHERE BinGrading = (#G1 + #G4 + #G7)
-- Alternatively...
--SELECT *
--FROM Product P
--JOIN Grading G ON P.Bingrading & G.BinScore > 0