Antonio Gallardo wrote:
Torsten Curdt dijo:
WHAT IS WRONG?
In example A all is OK.
In example B we are not using the power of the Database Manager.
WHY?
The LIMIT clause was designed to tell the database engine:
"Let find just X rows", then the database engine when it got the X
rows stop searching and return the X rows. It improves the response
time, since does not to continue searching!
Now think in a 10 million row table and YOU KNOW you need only 5 rows!
whether 10 million rows or not - the current sollution will only ask for
6 - one additional row. Is that the time penalty you are talking about?
Yes, because you already know that there are only 5 rows for every
register. Then the database will search the last 6th row that no exist.
Forcing to searh in the ENTIRE table.
No - why do you think the database searches the entire table?!?
...this is just a restriction on the resultset!
--
Torsten
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