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On 01/08/07 20:39, Tom Lane wrote:
> John Sales <spelunker334@yahoo.com> writes:
>> By doing this, I'm hoping that the query optimizer is smart
>> enough to see that if a query comes in and requests only the
>> six columns (that are in the narrower table) that PostgreSQL
>> won't have to load the wider table into the buffer pool, and
>> thereby actually have to only access about 10% the amount of
>> disk that it presently does.
>
>> Is this a sound theory?
>
> No. It still has to touch the second table to confirm the
> existence of rows to join to.
But if a query /requests *only* the six columns (that are in the
narrower table)/, why will the optimizer care about the other 224
columns?
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