Re: Is a "set current" TIMESTAMP operation atomic when updating/inserting multiple rows?
Hi, If u update this statment like what u have mentioned it will be updated for all the rows. update tablename set field name='2006-07-07 00:00:00'; Thanks & Regards Dilipkumar - Original Message - From: "Chris W" <[EMAIL PROTECTED]> To: "Dan Jakubiec" <[EMAIL PROTECTED]>; "MYSQL General List" Sent: Monday, July 24, 2006 1:11 AM Subject: Re: Is a "set current" TIMESTAMP operation atomic when updating/inserting multiple rows? Dan Jakubiec wrote: Hi. I want to insert/update multiple rows into a table which has a timestamp field, and I want to set the timestamp field in each row to the current timestamp. However, it is important to me that all the rows I update actually end up with the same timestamp value. My concern is: what happens if the SQL query take a long time and the current timestamp crosses a second boundary? For example, suppose I issue the following request on a very large table: UPDATE ts SET my_timestamp=NULL; Say that this query takes 3 seconds to complete. My questions: 1) Will all the rows have the same timestamp value? Or will some rows have "now", "now+1", and "now+2"? 2) Will the behavior be different if I use "my_timestamp=NOW()"? 3) If the timestamps will be different, what's the best way to make them all the same? In the manual it says that all calls to now() in a query always return the same time regardless of how many there are and how long it takes the query to run so I am thinking that all records with an auto update time stamp column that get changed in a single query would all have the same time stamp. It should be easy enough to test if you have a large set of data where an update would take a long time. I'm pretty sure it will do what you need though and set them all the same. -- Chris W KE5GIX Gift Giving Made Easy Get the gifts you want & give the gifts they want One stop wish list for any gift, from anywhere, for any occasion! http://thewishzone.com -- MySQL General Mailing List For list archives: http://lists.mysql.com/mysql To unsubscribe: http://lists.mysql.com/[EMAIL PROTECTED] ** DISCLAIMER ** Information contained and transmitted by this E-MAIL is proprietary to Sify Limited and is intended for use only by the individual or entity to which it is addressed, and may contain information that is privileged, confidential or exempt from disclosure under applicable law. If this is a forwarded message, the content of this E-MAIL may not have been sent with the authority of the Company. If you are not the intended recipient, an agent of the intended recipient or a person responsible for delivering the information to the named recipient, you are notified that any use, distribution, transmission, printing, copying or dissemination of this information in any way or in any manner is strictly prohibited. If you have received this communication in error, please delete this mail & notify us immediately at [EMAIL PROTECTED] Watch the latest updates on Mumbai, with video coverage of news, events, Bollywood, live darshan from Siddhivinayak temple and more, only on www.mumbailive.in Watch the hottest videos from Bollywood, Fashion, News and more only on www.sifymax.com -- MySQL General Mailing List For list archives: http://lists.mysql.com/mysql To unsubscribe:http://lists.mysql.com/[EMAIL PROTECTED]
Re: Is a "set current" TIMESTAMP operation atomic when updating/inserting multiple rows?
Ah, thanks Chris. I should have looked there (I was studying the TIMESTAMP sections, not NOW()). The NOW() documentation also refers to the SYSDATE() function which does the opposite (i.e. sets the time when the record actually gets added). So I'll go ahead and use the 'my_timestamp=NOW()' format in my queries. Out of curiosity, I wonder which of the two approaches 'my_timestamp=NULL' uses... NOW() or SYSDATE()? -- Dan In the manual it says that all calls to now() in a query always return the same time regardless of how many there are and how long it takes the query to run so I am thinking that all records with an auto update time stamp column that get changed in a single query would all have the same time stamp. It should be easy enough to test if you have a large set of data where an update would take a long time. I'm pretty sure it will do what you need though and set them all the same.
Re: Is a "set current" TIMESTAMP operation atomic when updating/inserting multiple rows?
Dan Jakubiec wrote: Hi. I want to insert/update multiple rows into a table which has a timestamp field, and I want to set the timestamp field in each row to the current timestamp. However, it is important to me that all the rows I update actually end up with the same timestamp value. My concern is: what happens if the SQL query take a long time and the current timestamp crosses a second boundary? For example, suppose I issue the following request on a very large table: UPDATE ts SET my_timestamp=NULL; Say that this query takes 3 seconds to complete. My questions: 1) Will all the rows have the same timestamp value? Or will some rows have "now", "now+1", and "now+2"? 2) Will the behavior be different if I use "my_timestamp=NOW()"? 3) If the timestamps will be different, what's the best way to make them all the same? In the manual it says that all calls to now() in a query always return the same time regardless of how many there are and how long it takes the query to run so I am thinking that all records with an auto update time stamp column that get changed in a single query would all have the same time stamp. It should be easy enough to test if you have a large set of data where an update would take a long time. I'm pretty sure it will do what you need though and set them all the same. -- Chris W KE5GIX Gift Giving Made Easy Get the gifts you want & give the gifts they want One stop wish list for any gift, from anywhere, for any occasion! http://thewishzone.com -- MySQL General Mailing List For list archives: http://lists.mysql.com/mysql To unsubscribe:http://lists.mysql.com/[EMAIL PROTECTED]
Is a "set current" TIMESTAMP operation atomic when updating/inserting multiple rows?
Hi. I want to insert/update multiple rows into a table which has a timestamp field, and I want to set the timestamp field in each row to the current timestamp. However, it is important to me that all the rows I update actually end up with the same timestamp value. My concern is: what happens if the SQL query take a long time and the current timestamp crosses a second boundary? For example, suppose I issue the following request on a very large table: UPDATE ts SET my_timestamp=NULL; Say that this query takes 3 seconds to complete. My questions: 1) Will all the rows have the same timestamp value? Or will some rows have "now", "now+1", and "now+2"? 2) Will the behavior be different if I use "my_timestamp=NOW()"? 3) If the timestamps will be different, what's the best way to make them all the same? Thanks in advance, -- Dan Jakubiec
