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Use of * affect the performance
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* Use of * affect the performance
@ 2006-01-16 14:49  Marcos <mjs_ops@gmx.net>
  0 siblings, 1 reply; 2+ messages in thread

From: Marcos @ 2006-01-16 14:49 UTC (permalink / raw)
  To: pgsql-performance

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




^ permalink  raw  reply  [nested|flat] 2+ messages in thread

* Re: Use of * affect the performance
@ 2006-01-16 21:55  Qingqing Zhou <zhouqq@cs.toronto.edu>
  parent: Marcos <mjs_ops@gmx.net>
  0 siblings, 0 replies; 2+ messages in thread

From: Qingqing Zhou @ 2006-01-16 21:55 UTC (permalink / raw)
  To: pgsql-performance


"Marcos" <mjs_ops@gmx.net> 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 





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