Just to clarify having key indexes of (a,b) or (b,a) have no difference ? On 11 Oct 2011, at 09:36, Johan De Meersman <vegiv...@tuxera.be> wrote:
> ----- Original Message ----- >> From: "Alex Schaft" <al...@quicksoftware.co.za> >> >> If you have a table with columns A & B, and might do a where on A or >> B, or an order by A, B, would single column indexes on A and B suffice >> or would performance on the order by query be improved by an index on >> A,B? > > Depends on usage :-) > > key (a, b) is good for "where a=.." or "where a=.. and b=.." > key (b, a) is good for "where b=.." or "where b=.. and a=.." > (note that the sequence of a and b in the where clause is not important) > key (a), key (b) is good for "where a=.." or "where b=.." but will only use > one index for "where a=.. and b=..". > > I think work is ongoing on having the parser use multiple indices, but I'm > not sure where that's at. > > > -- > Bier met grenadyn > Is als mosterd by den wyn > Sy die't drinkt, is eene kwezel > Hy die't drinkt, is ras een ezel > > -- > MySQL General Mailing List > For list archives: http://lists.mysql.com/mysql > To unsubscribe: > http://lists.mysql.com/mysql?unsub=neil.tompk...@googlemail.com > -- MySQL General Mailing List For list archives: http://lists.mysql.com/mysql To unsubscribe: http://lists.mysql.com/mysql?unsub=arch...@jab.org
