Torsten Curdt dijo: > 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
Because in the table with 10 millions are ONLY 5 rows that meet your WHERE clausule. you know that because this is a design issue. But setting "LIMIT 6" force the database to search the 6th row that you know does not exist. Then the question is: What do the database to try to find the 6th row? I think the answer is: scan the rest of the database after finding the ONLY 5 rows that already exist. --------------------------------------------------------------------- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, email: [EMAIL PROTECTED]
