On Oct 4, 4:44 pm, Captain Paralytic <paul_laut...@yahoo.com> wrote:
> On 4 Oct, 15:27, nk <nkoell...@gmail.com> wrote:
>
> > On Oct 4, 3:58 pm, Captain Paralytic <paul_laut...@yahoo.com> wrote:> Well,
> > > since your where clause operates on field2 of second_table, could you
> > > swap the tables round and use an index on field2 to limit the rows to
> > > be operated on?
>
> > > As it is, all the rows in main_table have to be read, a JOIN attempted
> > > into second_table and, if the JOIN is successful, field2 must be
> > > examined.
>
> > Wouldn't this prevent me from using the index on sort_field, though?
>
> Yes, but I don't know what the data looks like. It may be quicker to
> do a filesort than to have to read all the records in main_table.
>
> How many records in second_table have l.field2 = "abcde"?
Around 1 million.