Re: [HACKERS] Re: Multi field hash indexes
От | Bruce Momjian |
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Тема | Re: [HACKERS] Re: Multi field hash indexes |
Дата | |
Msg-id | 199803171905.OAA16761@candle.pha.pa.us обсуждение исходный текст |
Ответ на | Re: [HACKERS] Re: Multi field hash indexes (ocie@paracel.com) |
Ответы |
Re: [HACKERS] Re: Multi field hash indexes
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Список | pgsql-hackers |
> 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. -- Bruce Momjian | 830 Blythe Avenue maillist@candle.pha.pa.us | Drexel Hill, Pennsylvania 19026 + If your life is a hard drive, | (610) 353-9879(w) + Christ can be your backup. | (610) 853-3000(h)
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