http://www.pythian.com/news/374/mysql-group-by-and-distinct-oddity/ News and views from Pythian DBAs Fri, 10 Feb 2012 13:01:25 +0000 hourly 1 http://wordpress.org/?v=3.0.4 http://www.pythian.com/news/374/mysql-group-by-and-distinct-oddity/#comment-16199 Alex Gorbachev Mon, 22 Jan 2007 14:21:35 +0000 http://www.pythian.com/blogs/374/mysql-group-by-and-distinct-oddity#comment-16199 Explanation is simple. Oracle isn't smart but just follows the rules. The rule in this case - expression in order by must consist of selected columns/expressions. This should work I believe: <code> select distinct substr(privilege,1,2) from user_tab_privs_recd order by substr(substr(privilege,1,2),1,1) </code> Explanation is simple. Oracle isn’t smart but just follows the rules. The rule in this case – expression in order by must consist of selected columns/expressions. This should work I believe:

select distinct substr(privilege,1,2)
from user_tab_privs_recd
order by substr(substr(privilege,1,2),1,1)


]]> http://www.pythian.com/news/374/mysql-group-by-and-distinct-oddity/#comment-16110 Gary Mon, 22 Jan 2007 04:00:40 +0000 http://www.pythian.com/blogs/374/mysql-group-by-and-distinct-oddity#comment-16110 Whoops. Meant to say THIS one works: select distinct privilege from user_tab_privs_recd order by substr(privilege,1,3); This one doesn't select distinct substr(privilege,1,2) from user_tab_privs_recd order by substr(privilege,1,1) so there are limits to its smarts. Whoops. Meant to say
THIS one works:
select distinct privilege from user_tab_privs_recd order by substr(privilege,1,3);
This one doesn’t
select distinct substr(privilege,1,2) from user_tab_privs_recd
order by substr(privilege,1,1)
so there are limits to its smarts.

]]> http://www.pythian.com/news/374/mysql-group-by-and-distinct-oddity/#comment-16109 Gary Mon, 22 Jan 2007 03:58:00 +0000 http://www.pythian.com/blogs/374/mysql-group-by-and-distinct-oddity#comment-16109 Interestingly, Oracle applies some smarts too. The following works fine: select distinct substr(privilege,1,2) from user_tab_privs_recd order by substr(privilege,1,2); but this fails: select distinct substr(privilege,1,2) from user_tab_privs_recd order by substr(privilege,1,3); Oracle actually works out whether it can derive the order by expression from the selected expression, rather than simply ruling out anything that isn't actually selected. Interestingly, Oracle applies some smarts too.
The following works fine:
select distinct substr(privilege,1,2) from user_tab_privs_recd
order by substr(privilege,1,2);
but this fails:
select distinct substr(privilege,1,2) from user_tab_privs_recd
order by substr(privilege,1,3);
Oracle actually works out whether it can derive the order by expression from the selected expression, rather than simply ruling out anything that isn’t actually selected.

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