Without an ORDER BY, there is no order.
Any order you see is purely accidental.
If no order is requested, how could it be quicker to read through the
index, and jump madly about the table extracting small records from
large buffers.
A linear read from the table is much faster.
Andrey Hristov wrote:
----- Original Message -----
From: "gerald_clark" <[EMAIL PROTECTED]>
To: "Andrey Hristov" <[EMAIL PROTECTED]>
Cc: <[EMAIL PROTECTED]>
Sent: Wednesday, October 23, 2002 6:23 PM
Subject: Re: Problem with select.
Andrey Hristov wrote:
HI,
I don't know is it bad or not but I face queries the work quite long
time.
the sql is :
select * from log_answers_index limit 0,10
and it takes too much time for me to receive the result.
I got indexes on most of the fields, i got primary key which is
auto_increment int(11). When I did explain on the query I got this :
type : ALL
rows : 123010
all other cells are empty.
When I do :
select * from log_answers_index where log_entry_index between 1 and 10
i got type : range
For me it is strange that the primary key is not used when there is LIMIT
What would be the point?
Without a WHERE or an ORDER BY, using an index would slow it down.
I am not an expert but I think that when there is not order by the output is
sorted on the primary key.
So : select * from log_answers_index limit 0,10 and select * from
log_ansers_index where log_entry_id between 1 and 10
are no different in the output. But yes as internal work (of mysql) it is
quite different.
I think that will be useful optimization done by the optimizer.
Andrey
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