Hi Douglas,
I need to know the number of rows that a query will return before actually executing the query. So I am sending select count(*) before sending select *. Actually I need to reject queries if the number of records that it will return is huge, to avoid my server running out of memory. My application has a huge database of around 10 millions. The selects with INNODB falls drastically as the size of records grow. A select count(*) that takes 4 secs with 1 million records takes 40 secs with 3 million records. Regards Prasad -----Original Message----- From: Douglas Sims [mailto:[EMAIL PROTECTED] Sent: Thursday, September 07, 2006 10:39 AM To: Prasad Ramisetti (WT01 - Broadband Networks) Cc: MySQL List Subject: Re: problem with InnoDB Hi Prasad A primary key automatically creates an index and not-null and unique constraints, too. So you don't need to explicitly create an index on a primary key column. If your queries are going to have WHERE clauses (as they most likely are) I'm not sure how the small-index suggestion would make the query any faster - the WHERE clause would preclude the use of that index in computing the rows - but I'm probably missing something here. When you say that you need to know the number of rows returned before executing the query, do you mean before you start getting rows back or before you actually execute the query? I don't think it's possible to know how many rows the query will return without actually executing it, but you might well want to know how many rows you get before you start processing rows. Have you looked at the SQL_CALC_FOUND_ROWS option on SELECT, and the accompanying FOUND_ROWS() function? http://dev.mysql.com/doc/refman/ 5.0/en/information-functions.html It will tell you the total number of rows which would have been found if you hadn't used a LIMIT clause. I think it is a connection- specific function; if you created a second statement handle and did a SELECT FOUND_ROWS() on the same connection, perhaps that would give what you want. Douglas Sims [EMAIL PROTECTED] On Sep 6, 2006, at 11:29 PM, <[EMAIL PROTECTED]> <[EMAIL PROTECTED]> wrote: > > Hi Dan, > > Thanks for yur response. Does it makes sense to create an index on a > primary key ..as that is my smallest field ? > > Regards > Prasad > > -----Original Message----- > From: Dan Nelson [mailto:[EMAIL PROTECTED] > Sent: Monday, September 04, 2006 9:53 AM > To: Prasad Ramisetti (WT01 - Broadband Networks) > Cc: [EMAIL PROTECTED]; mysql@lists.mysql.com > Subject: Re: problem with InnoDB > > In the last episode (Sep 04), [EMAIL PROTECTED] said: >> Actually there is some requirement, where I need to know the number >> of > >> rows that I will get for my queries before actually executing the >> query. Could you please suggest some way for this. > > Your best bet is to create an index on the smallest column you can > find (maybe even create a char(1) and leave it empty), and "SELECT > COUNT(*) FROM innotable USE INDEX (smallcolumn)". That way mysql only > has to scan a small secondary index instead of the main table index. > > -- > Dan Nelson > [EMAIL PROTECTED] > > > The information contained in this electronic message and any > attachments to this message are intended for the exclusive use of the > addressee(s) and may contain proprietary, confidential or privileged > information. If you are not the intended recipient, you should not > disseminate, distribute or copy this e-mail. Please notify the sender > immediately and destroy all copies of this message and any > attachments. > > WARNING: Computer viruses can be transmitted via email. The recipient > should check this email and any attachments for the presence of > viruses. The company accepts no liability for any damage caused by any > virus transmitted by this email. > > www.wipro.com > > -- > MySQL General Mailing List > For list archives: http://lists.mysql.com/mysql > To unsubscribe: http://lists.mysql.com/[EMAIL PROTECTED] > The information contained in this electronic message and any attachments to this message are intended for the exclusive use of the addressee(s) and may contain proprietary, confidential or privileged information. If you are not the intended recipient, you should not disseminate, distribute or copy this e-mail. Please notify the sender immediately and destroy all copies of this message and any attachments. WARNING: Computer viruses can be transmitted via email. The recipient should check this email and any attachments for the presence of viruses. The company accepts no liability for any damage caused by any virus transmitted by this email. www.wipro.com -- MySQL General Mailing List For list archives: http://lists.mysql.com/mysql To unsubscribe: http://lists.mysql.com/[EMAIL PROTECTED]
