Re: [HACKERS] Re: Multi field hash indexes

> I was originally thinking that this would be supported like the btree
> indexes are now -- an index on (a,b,c,d) serves as in index on a,
> (a,b), (a,b,c) and (a,b,c,d), but it doesn't serve as an index on b,
> or (b,c), etc. My original idea was that the first item in the index
> would define a hash table whose entries were hash tables on the second
> item, etc. I now think that this would waste quite a bit of space,
> and would have the same restriction as btrees, which is unnatural.

This is a standard restriction. If you need an index on a lower-level
field, create one. I don't think you are going to be able to improve on
(a,b), (a,b,c). If you allowed (b,c) that is another index.

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