Re: [Python-sybase-misc] How to set Sybase sets/tuples from Python?

[Nick E. <ne...@gm...>]

I was under the impression that repeat use of a query was for performance
given this in the documentation of execute:

The prepared dynamic SQL will be reused by the cursor if the same SQL is
passed in the sql argument. This is most effective for algorithms where the
same operation is used, but different parameters are bound to it (many
times).

If the parameters are not being used for performance though, how is your
solution superior to the naive:
query = 'select foo from bar where baz in %s'
types = ('A', 'B', 'C')
cursor.execute(query % types)

which is more transparent.

If the performance gains are of significance from repeat use of a query,
your solution has the advantage that the cursor will reuse the prepared
dynamic SQL for the 2nd+ time using any particular number of items.

Nick


On Tue, Aug 18, 2009 at 10:27 AM, Deron Meranda <der...@gm...>wrote:

> On Tue, Aug 18, 2009 at 11:19 AM, Nick Edds<ne...@gm...> wrote:
> > But what if later you want to run the query with items = ['A', 'B', 'C',
> > 'D']?
> >
> > Then you're going to need to construct a new query because the original
> > query can only support 3 items., so you lose the performance gain of
> making
> > a query that takes parameters. I can't really see a better solution
> though.
>
> Constructing the query and args dict using the list comprehension
> methods I showed will equally work for any sized list of items (>=1)
> without changing any python code.
>
> As far as I'm aware the substitution mechanism in the DBI is not
> there for performance; but is primarily there to make it easier to use,
> to facilitate automatic type conversions, and to help prevent mistakes
> in escaping and quoting SQL literals.
>
> I suspect any performance loss or gain will be negligible.
> --
> Deron Meranda
>