Mysql Multiple Primary Keys + Indexing?

[ToshiroOC]

I am currently figuring out which tables have what in them for an application I'm writing as an excercise, and I have a bunch of tables that look like this:

$query = 'create table assignedgroups (
            userid int unsigned not null,
            groupid int unsigned not null,
            primary key (userid, groupid)
            )';
$result = mysql_query( $query ); 

My question is this: If I'm declaring the primary key to be (userid, groupid), does that automatically mean that both my userid column and my groupid column will be indexed? If not, what should I add to the columns to have them indexed? I searched through the Mysql manual, but I must have missed it. Thanks for your time

-ToshiroOC

[r937]

declaring (userid,groupid) as the primary key will create a compund index

if you wanted to retrieve the groupids for a given userid=foo, the index would be used

but if you wanted the userids for a given groupid=bar, the index might not be used, since you'd have to get every index entry

you might want to add an index on groupid, or perhaps on (groupid,userid)

another consideration is whether there are any other columns in the table besides those two

rudy
http://r937.com/

[ToshiroOC]

I'll go with key(groupid, userid) and see if that works. Thanks for your help!