| From: | Markus Schaber <schabi(at)logix-tt(dot)com> |
|---|---|
| To: | pgsql-performance(at)postgresql(dot)org |
| Cc: | pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: qsort again (was Re: [PERFORM] Strange Create Index |
| Date: | 2006-02-17 10:13:41 |
| Message-ID: | 43F5A1D5.20903@logix-tt.com |
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| Lists: | pgsql-hackers pgsql-performance |
Hi, David,
David Lang schrieb:
>> In SQL_ASCII, just take the first 4 characters (or 8, if using a 64-bit
>> sortKey as elsewhere suggested). The sorting key doesn't need to be a
>> one-to-one mapping.
> that would violate your second contraint ( f(a)==f(b) iff (a==b) )
no, it doesn't.
When both strings are equal, then the first characters are equal, too.
If they are not equal, the constraint condition does not match.
The first characters of the strings may be equal as f(a) may be equal to
f(b) as to the other constraint.
Markus
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