List:General Discussion« Previous MessageNext Message »
From:Alec.Cawley Date:October 3 2005 10:34am
Subject:Re: Double indexes on one field
View as plain text  
Yannick Warnier <ywarnier@stripped> wrote on 03/10/2005 11:18:05:

> Hi all,
> 
> Using PhpMyAdmin, I seldom get the warning message:
> PRIMARY and INDEX keys should not both be set for column `ID`
> 
> I understand its meaning, but I was wondering to what extent having a
> field indexed AND being a primary key might slow down/speed up my
> queries.
> 
> Is that gonna take twice the time if I am searching on the ID field,
> just because there are two indexes?
> 
> I'd like to have a rough idea of how serioulsy I need to avoid these.

It will not slow down your searches at all, but it will slow down your 
inserts. Since a PRIMARY KEY is a UNIQUE index that happens to have been 
declared to be primary, you are simply storing the same information twice. 
I cannot think of any possible benefit in having two identical indexes on 
a table, and there is a cost to maintaining two index trees.

        Alec
 

Thread
Double indexes on one fieldYannick Warnier3 Oct
  • Re: Double indexes on one fieldMartijn Tonies3 Oct
    • Re: Double indexes on one fieldYannick Warnier3 Oct
      • Re: Double indexes on one fieldBastian Balthazar Bux3 Oct
        • Re: Double indexes on one fieldYannick Warnier3 Oct
  • Re: Double indexes on one fieldAlec.Cawley3 Oct