Re: [Skunkworks] MySQL question: create table if not exists
@steve - you're right about the permission issues and the SELECT can be a good workaround @peter - why are you writing SQL from a program? Presumably, whatever framework you're using has abstracted this stuff out, no? -- Kili.io - OpenStack for Africa: kili.io Musings: twitter.com/varud <https://twitter.com/varud> About Adam: www.linkedin.com/in/adamcnelson On Wed, Oct 23, 2013 at 5:02 PM, Steve Obbayi <steve@sobbayi.com> wrote:
Depending on the situation one can run into unexpected occurrences reading the information schema because of permissions. In short for a general user you cannot access all table meta data from that schema without proper rights... you are restricted to only some of it otherwise you get NULLs all over the place. Then again there is the significantly additional overhead reading from the info schema, but again this can be argued away in dozens of ways. Doing a simple select is the least painful of course unless the table exists and has a gazillion rows :) so running a query like SELECT 1 FROM table LIMIT 0,1 becomes the least expensive option to verify existence of a table in MySQL.
------------------------------
*From: *"Adam Nelson" <adam@varud.com>
*To: *"Skunkworks Mailing List" <skunkworks@lists.my.co.ke> *Sent: *Miércoles, 23 de Octubre 2013 14:08:36
*Subject: *Re: [Skunkworks] MySQL question: create table if not exists
Nonetheless, if you want to know if a table exists, the proper place to look is in the information_schema database or if for some reason you can't look there, run `show tables;` from within the database you're checking.
There's no need to touch the table in order to evaluate its existence.
-- Kili.io - OpenStack for Africa: kili.io Musings: twitter.com/varud <https://twitter.com/varud> About Adam: www.linkedin.com/in/adamcnelson
On Wed, Oct 23, 2013 at 4:01 PM, Steve Obbayi <steve@sobbayi.com> wrote:
Yes really @Rad its the resource that returns NULL and not the table row, don't mix the two. By the way 'id' is the name of any column in the table and not 'id' persay so in essence..
SELECT any_row from table;
should return the rows or 0 rows if the table exists. By calling the affected_rows function in the mysql api one can clarify that. NULL is returned when mysql doesnt find the table to select from.
------------------------------
*From: *"Rad!" <conradakunga@gmail.com> *To: *"Skunkworks Mailing List" <skunkworks@lists.my.co.ke> *Sent: *Miércoles, 23 de Octubre 2013 12:19:37 *Subject: *Re: [Skunkworks] MySQL question: create table if not exists
@steve really? What if the value for ID is actually null?
On Wed, Oct 23, 2013 at 1:32 PM, Steve Obbayi <steve@sobbayi.com> wrote:
Yes it starts with the SELECT then executes the CREATE... IF NOT EXISTS is simply meant to suppress errors that the table already exists and from an execution stand point it is no different than if it was left out. In short CREATE always checks if the table exists before creating it
In addition to your solution you can also run a simple query directly on the table (SELECT Id FROM table ) and if it returns NULL then the table doesn't exist so you can proceed and create it
------------------------------
*From: *"Peter Karunyu" <pkarunyu@gmail.com <pkarunyu@gmail...com>> *To: *"Skunkworks forum" <skunkworks@lists.my.co.ke> *Sent: *Miércoles, 23 de Octubre 2013 10:38:07 *Subject: *[Skunkworks] MySQL question: create table if not exists
Dear MySQL gurus,
So I have this query:
*CREATE TABLE IF NOT EXISTS my_table_a ( SELECT * FROM my_table_b WHERE some_column=some_value);*
My question is, how does MySQL evaluate it? Does it start with the SELECT * then goes to check if that table exists, then creates the table?
The reason I am asking is because the *SELECT * FROM my_table_b WHERE some_column=some_value *part is particularly nasty and takes forever, and therefore, I was thinking of splitting it into two thus:
1. $x = SELECT COUNT(1) FROM information_schema.tables WHERE table_schema='my_db' AND table_name='my_table_a' 2. if ( ! $x ) { CREATE TABLE my_table_a ( SELECT * FROM my_table_b WHERE some_column=some_value); }
And therefore, possibly save a few seconds.
Or am I searching for speed in the wrong place?
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@Adam, yes, the framework I use (CodeIgniter) allows usage of ActiveRecord and a variety of other third party ORMs. I wrote the queries herein to make it easier to explain my situation. On the (de)merits of using ORMs and other database abstractions, I believe thats a *discussion* for another day :-) On Wed, Oct 23, 2013 at 5:23 PM, Adam Nelson <adam@varud.com> wrote:
@steve - you're right about the permission issues and the SELECT can be a good workaround
@peter - why are you writing SQL from a program? Presumably, whatever framework you're using has abstracted this stuff out, no?
-- Kili.io - OpenStack for Africa: kili.io Musings: twitter.com/varud <https://twitter.com/varud> About Adam: www.linkedin.com/in/adamcnelson
On Wed, Oct 23, 2013 at 5:02 PM, Steve Obbayi <steve@sobbayi.com> wrote:
Depending on the situation one can run into unexpected occurrences reading the information schema because of permissions. In short for a general user you cannot access all table meta data from that schema without proper rights... you are restricted to only some of it otherwise you get NULLs all over the place. Then again there is the significantly additional overhead reading from the info schema, but again this can be argued away in dozens of ways. Doing a simple select is the least painful of course unless the table exists and has a gazillion rows :) so running a query like SELECT 1 FROM table LIMIT 0,1 becomes the least expensive option to verify existence of a table in MySQL.
------------------------------
*From: *"Adam Nelson" <adam@varud.com>
*To: *"Skunkworks Mailing List" <skunkworks@lists.my.co.ke> *Sent: *Miércoles, 23 de Octubre 2013 14:08:36
*Subject: *Re: [Skunkworks] MySQL question: create table if not exists
Nonetheless, if you want to know if a table exists, the proper place to look is in the information_schema database or if for some reason you can't look there, run `show tables;` from within the database you're checking.
There's no need to touch the table in order to evaluate its existence.
-- Kili.io - OpenStack for Africa: kili.io Musings: twitter.com/varud <https://twitter.com/varud> About Adam: www.linkedin.com/in/adamcnelson
On Wed, Oct 23, 2013 at 4:01 PM, Steve Obbayi <steve@sobbayi.com> wrote:
Yes really @Rad its the resource that returns NULL and not the table row, don't mix the two. By the way 'id' is the name of any column in the table and not 'id' persay so in essence..
SELECT any_row from table;
should return the rows or 0 rows if the table exists. By calling the affected_rows function in the mysql api one can clarify that. NULL is returned when mysql doesnt find the table to select from.
------------------------------
*From: *"Rad!" <conradakunga@gmail.com> *To: *"Skunkworks Mailing List" <skunkworks@lists.my.co.ke> *Sent: *Miércoles, 23 de Octubre 2013 12:19:37 *Subject: *Re: [Skunkworks] MySQL question: create table if not exists
@steve really? What if the value for ID is actually null?
On Wed, Oct 23, 2013 at 1:32 PM, Steve Obbayi <steve@sobbayi.com> wrote:
Yes it starts with the SELECT then executes the CREATE... IF NOT EXISTS is simply meant to suppress errors that the table already exists and from an execution stand point it is no different than if it was left out. In short CREATE always checks if the table exists before creating it
In addition to your solution you can also run a simple query directly on the table (SELECT Id FROM table ) and if it returns NULL then the table doesn't exist so you can proceed and create it
------------------------------
*From: *"Peter Karunyu" <pkarunyu@gmail.com <pkarunyu@gmail...com>> *To: *"Skunkworks forum" <skunkworks@lists.my.co.ke> *Sent: *Miércoles, 23 de Octubre 2013 10:38:07 *Subject: *[Skunkworks] MySQL question: create table if not exists
Dear MySQL gurus,
So I have this query:
*CREATE TABLE IF NOT EXISTS my_table_a ( SELECT * FROM my_table_b WHERE some_column=some_value);*
My question is, how does MySQL evaluate it? Does it start with the SELECT * then goes to check if that table exists, then creates the table?
The reason I am asking is because the *SELECT * FROM my_table_b WHERE some_column=some_value *part is particularly nasty and takes forever, and therefore, I was thinking of splitting it into two thus:
1. $x = SELECT COUNT(1) FROM information_schema.tables WHERE table_schema='my_db' AND table_name='my_table_a' 2. if ( ! $x ) { CREATE TABLE my_table_a ( SELECT * FROM my_table_b WHERE some_column=some_value); }
And therefore, possibly save a few seconds.
Or am I searching for speed in the wrong place?
_______________________________________________ skunkworks mailing list skunkworks@lists.my.co.ke ------------ List info, subscribe/unsubscribe http://lists.my.co.ke/cgi-bin/mailman/listinfo/skunkworks ------------
Skunkworks Rules http://my.co.ke/phpbb/viewtopic.php?f=24&t=94 ------------ Other services @ http://my.co.ke
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-- Regards, Peter Karunyu -------------------
I can't imagine that a mature framework like CodeIgniter would touch the table in order to check for the existence of that table. -- Kili.io - OpenStack for Africa: kili.io Musings: twitter.com/varud <https://twitter.com/varud> About Adam: www.linkedin.com/in/adamcnelson On Wed, Oct 23, 2013 at 5:34 PM, Peter Karunyu <pkarunyu@gmail.com> wrote:
@Adam, yes, the framework I use (CodeIgniter) allows usage of ActiveRecord and a variety of other third party ORMs. I wrote the queries herein to make it easier to explain my situation.
On the (de)merits of using ORMs and other database abstractions, I believe thats a *discussion* for another day :-)
On Wed, Oct 23, 2013 at 5:23 PM, Adam Nelson <adam@varud.com> wrote:
@steve - you're right about the permission issues and the SELECT can be a good workaround
@peter - why are you writing SQL from a program? Presumably, whatever framework you're using has abstracted this stuff out, no?
-- Kili.io - OpenStack for Africa: kili.io Musings: twitter.com/varud <https://twitter.com/varud> About Adam: www.linkedin.com/in/adamcnelson
On Wed, Oct 23, 2013 at 5:02 PM, Steve Obbayi <steve@sobbayi.com> wrote:
Depending on the situation one can run into unexpected occurrences reading the information schema because of permissions. In short for a general user you cannot access all table meta data from that schema without proper rights... you are restricted to only some of it otherwise you get NULLs all over the place. Then again there is the significantly additional overhead reading from the info schema, but again this can be argued away in dozens of ways. Doing a simple select is the least painful of course unless the table exists and has a gazillion rows :) so running a query like SELECT 1 FROM table LIMIT 0,1 becomes the least expensive option to verify existence of a table in MySQL.
------------------------------
*From: *"Adam Nelson" <adam@varud.com>
*To: *"Skunkworks Mailing List" <skunkworks@lists.my.co.ke> *Sent: *Miércoles, 23 de Octubre 2013 14:08:36
*Subject: *Re: [Skunkworks] MySQL question: create table if not exists
Nonetheless, if you want to know if a table exists, the proper place to look is in the information_schema database or if for some reason you can't look there, run `show tables;` from within the database you're checking.
There's no need to touch the table in order to evaluate its existence.
-- Kili.io - OpenStack for Africa: kili.io Musings: twitter.com/varud <https://twitter.com/varud> About Adam: www.linkedin.com/in/adamcnelson
On Wed, Oct 23, 2013 at 4:01 PM, Steve Obbayi <steve@sobbayi.com> wrote:
Yes really @Rad its the resource that returns NULL and not the table row, don't mix the two. By the way 'id' is the name of any column in the table and not 'id' persay so in essence..
SELECT any_row from table;
should return the rows or 0 rows if the table exists. By calling the affected_rows function in the mysql api one can clarify that. NULL is returned when mysql doesnt find the table to select from.
------------------------------
*From: *"Rad!" <conradakunga@gmail.com> *To: *"Skunkworks Mailing List" <skunkworks@lists.my.co.ke> *Sent: *Miércoles, 23 de Octubre 2013 12:19:37 *Subject: *Re: [Skunkworks] MySQL question: create table if not exists
@steve really? What if the value for ID is actually null?
On Wed, Oct 23, 2013 at 1:32 PM, Steve Obbayi <steve@sobbayi.com>wrote:
Yes it starts with the SELECT then executes the CREATE... IF NOT EXISTS is simply meant to suppress errors that the table already exists and from an execution stand point it is no different than if it was left out. In short CREATE always checks if the table exists before creating it
In addition to your solution you can also run a simple query directly on the table (SELECT Id FROM table ) and if it returns NULL then the table doesn't exist so you can proceed and create it
------------------------------
*From: *"Peter Karunyu" <pkarunyu@gmail.com <pkarunyu@gmail...com>> *To: *"Skunkworks forum" <skunkworks@lists.my.co.ke> *Sent: *Miércoles, 23 de Octubre 2013 10:38:07 *Subject: *[Skunkworks] MySQL question: create table if not exists
Dear MySQL gurus,
So I have this query:
*CREATE TABLE IF NOT EXISTS my_table_a ( SELECT * FROM my_table_b WHERE some_column=some_value);*
My question is, how does MySQL evaluate it? Does it start with the SELECT * then goes to check if that table exists, then creates the table?
The reason I am asking is because the *SELECT * FROM my_table_b WHERE some_column=some_value *part is particularly nasty and takes forever, and therefore, I was thinking of splitting it into two thus:
1. $x = SELECT COUNT(1) FROM information_schema.tables WHERE table_schema='my_db' AND table_name='my_table_a' 2. if ( ! $x ) { CREATE TABLE my_table_a ( SELECT * FROM my_table_b WHERE some_column=some_value); }
And therefore, possibly save a few seconds.
Or am I searching for speed in the wrong place?
_______________________________________________ skunkworks mailing list skunkworks@lists.my.co.ke ------------ List info, subscribe/unsubscribe http://lists.my.co.ke/cgi-bin/mailman/listinfo/skunkworks ------------
Skunkworks Rules http://my.co.ke/phpbb/viewtopic.php?f=24&t=94 ------------ Other services @ http://my.co.ke
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-- Regards, Peter Karunyu -------------------
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participants (2)
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Adam Nelson -
Peter Karunyu