Hannes Ricklefs
<[EMAIL PROTECTED]> wrote:
I am wondering at what stage the actual SQL gets executed. Is that
the first call to step? or does the sql get executed for each step
call?
I'm not sure what you mean by "executed". Prepare generates an execution
plan. With each call to step, this execution plan is carried out until
one row is available.
I am thinking that the average call to step should be the same no
matter how big the database is?!
I guess this depends on how you define the set you are averaging over.
Even within the same database, time taken by a call to step may vary
widely. Consider:
select * from table;
You get the records from table in no particular order. Every step call
will take approximately the same time, independent of the size of the
table.
select * from table
order by someField;
Assuming there is no index on someField, this query requires retrieving
all records from table into memory and sorting them there before the
first row can be produced. As a result, the first step can take a long
time, proportional to NlogN where N is the number of records, whereas
subsequent steps are fast.
Igor Tandetnik
