Обсуждение: Use of * affect the performance

От:
Marcos
Дата:

Hi,

I always think that use of * in SELECT affected in the performance,
becoming the search slowest.

But I read in the a Postgres book's that it increases the speed of
search.

And now???? What the more fast?

Thanks


От:
"Qingqing Zhou"
Дата:

"Marcos" <> wrote
>
> I always think that use of * in SELECT affected in the performance,
> becoming the search slowest.
>
> But I read in the a Postgres book's that it increases the speed of
> search.
>
> And now???? What the more fast?
>

If you mean use "*" vs. "explicitely name all columns of a relation", then
there is almost no difference except the negligible difference in parsing.
If you mean you just want part of the columns of a relation but you still
use "*": Yes, you will save one projection operation for each result row but
you will pay for more network traffic. In the worst case, say your "*"
involves some toast attributes, you just hurt performance. Considering the
benefits is so marginal and dangerous, I suggest stay with the idea that
"only retrive the columns that you are interested in".

Regards,
Qingqing