Hi, The optimizer currently only estimates the cost (roughly the number of I/O operations). It doesn't estimate the number of rows separately.
Regards, Thomas On Mon, Jan 6, 2014 at 8:22 AM, Noel Grandin <[email protected]> wrote: > > > On 2014-01-03 05:24, Felix Xu wrote: > >> Hi, >> Cardinality estimation is a widely used technique in databases for >> selecting the best execution plan, is there any >> implementation in H2 ? I'm also wondering how does the table statistics >> data used in H2? I want to get the estimated row >> numbers of the output dataset of each operator(join/group by etc.) in a >> query, which part of code should I get started with? >> >> > We currently only do very basic selectivity estimation. > The relevant code lives in > org.h2.command.ddl.Analyze > > > -- > You received this message because you are subscribed to the Google Groups > "H2 Database" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To post to this group, send email to [email protected]. > Visit this group at http://groups.google.com/group/h2-database. > For more options, visit https://groups.google.com/groups/opt_out. > -- You received this message because you are subscribed to the Google Groups "H2 Database" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/h2-database. For more options, visit https://groups.google.com/groups/opt_out.
