Aggregate bitwise-OR in a subquery

Question

Given the following table:

CREATE TABLE BitValues ( n int )

Is it possible to compute the bitwise-OR of n for all rows with

Answer 1

You can use a variable and do a "bitwise or" (|) for each row:

declare @t table (n int)
insert @t select 1 union select 2 union select 4

declare @i int
set @i = 0

select  @i = @i | n
from    @t

select @i

This prints 7. Note that assigning variables in a select is not officially supported.

In a more strictly SQL way, you can create a table with one row for each bit. This table would have 31 rows, as the 32nd bit is a negative integer. This example uses a recursive CTE to create that table:

declare @t table (n int)
insert @t select 1 union select 2 union select 3

; with bits(nr, pow) as 
(
    select  1
    ,       1
    union all
    select  nr + 1
    ,       pow * 2
    from    bits
    where   nr <= 30
)
select  sum(b.pow)
from    bits b
where   exists
        (
        select  *
        from    @t t  
        where   b.pow & t.n > 0
        )

This sums the bits where any bit in the source table is set.