"Brandon, Nicholas (UK)" <[EMAIL PROTECTED]> wrote: > > > select .... > > > FROM instances as i > > > inner join instance_fields as count using(instanceid) > > > inner join instance_fields as first using (instanceid) > > > inner join instance_fields as last using (instanceid) > > > inner join instance_fields as severity using (instanceid) > > > inner join instance_fields as summary using (instanceid) > > > inner join instance_fields as node using (instanceid) > > > inner join instance_fields as source using (instanceid) > > I don't want to hijack this thread (not too much anyway) but this got me > thinking about JOINs since I have a database that uses a similar concept > (one table holds a number of key-value pairs for another). > > As I understand it, an INNER JOIN is equivalent in pseudo-code to: > > For (every record in table A) > for (every record in table B) > for (...) > > where another for loop is added with each additional JOIN. > > Using Christian's example, would SQLite use the pseudo-code represented > above or does it use some intelligence that all the JOINs are from the > same table and hence the pseudo-code is: > > for (every record in table "instances") > for (every record in table "instance_fields") >
It does a nested loop. There is no optimization for when the same table is joined multiple times. How often does that happy, really? -- D. Richard Hipp <[EMAIL PROTECTED]>
