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Re: [PROGRAMMERING] [Database] Transaktioner med eller uden optællingsfelt?



On Tue, 10 Aug 2004 23:32:51 +0200, donald_j_axel wrote:

> 
> Er der ikke i PostgreSQL funktionalitet til at vedligeholde
> tæller-felter? Enten ved "user-defined functions" eller er der en
> indbygget funktion for netop dette almindelige formål? Jeg har ikke tid
> at slå op, desværre, men PostgreSQL er vældig godt dokumenteret. Det er
> MySQL også.
> 
Man kan lave en sequence eller en stored procedure. Stored procedures er
vist også understøttet i MySQL >3.
> Det er et performance spørgsmål. Hvis
du skal gennemtrawle 100000
> records for at tælle lager op, så tager det lidt længere tid;-)
I SQL tager en count(tuple) altså ikke lang tid, da database selv ved,
hvor mange rækker en tabel har. Hvis optællingen har med et subset af en
tabel at gøre, kan man øge hastigheden ved at oprette et index på
tuplen.

-- 
Hilsen/Regards
Michael Rasmussen

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