Re: Btree index extension question

fcanedo(at)hotpop(dot)com wrote:

>
>If postgresql does bitwise operations, then you can use that instead of
>defining new operators. Just construct a number for all the columns that
>need to be true and do a bitwise 'and' with the stored value. (eg. (7 &
>stored_val) = 7)
>

Yeah... The thing is that I want to be able to the index. And to use the
index, I need BOOLEAN
operators (this seems to be the LEAST of my problems,but anyway) - so, I
have to define 'wrappers' around the standard bitwise operations - e.g.
a <<= b ---> a & b = a;

>
>
>If postgresql uses an index to supply functions with their parameters,
>then make a function that'll do the comparison for you and use it in your
>query.
>

Well ... that's the point - can't do that :-(
You can create functional indexes in postgres (and anywhere else AFAIK),
but the function must take a SINGLE parameter.
In other words, the only way to do what I need would be to create 15
functions, like:
check_bit_1 (x) return x & 1 = 1;
check_bit_2 (x) return x & 2 = 2;
etc...
And then create 15 different indexes (one for each func).

But even that would not be of much help, because I need to search by a
COMBINATION of
parameters, and need a COMPOUND index to do that, not a separate index
for each attr...

> Or make the index (on all the columns) and make a function that
>takes all the columns as the parameters to compare against (and ofcourse
>the values that you want to check against). That way you always use the
>columns of the index in the correct order.
>

I am not sure I understand this suggestion... If I make the index on all
the columns, I would need to specify all the (leftmost) values in the
search criteria to be able to use it, right?
For example, suppose, I have an index on (a,b,c) - then
select * from foo where a=bar and b=bar will work, but
select * from foo where b=bar and c=bar will not...

That's exactly my problem - I need to be able to search by any
combination of the values - (a),(b),(c),(ab),(ac),(bc),(abc)
... only I have 15 of them - too many combinations to consider buidling
indexes for any of them :-(