id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
9136	Oracle backend: slicing is using row_number() instead of rownum	Guillaume Taglang <guillaume.taglang@…>	nobody	"Doing Entity.objects.all()[:10] is generating a query like:
{{{
SELECT *
FROM   (SELECT (ROW_NUMBER() OVER (ORDER BY ""ENTITY"".""ID"")) AS ""_RN"",
               ""ENTITY"".""ID"", ""ENTITY"".""NAME""
        FROM   ""ENTITY"")
WHERE  ""_RN"" > 0
AND    ""_RN"" <= 10
}}}
This is suboptimal as a full table scan is forced (at least in 10g).
Using ''rownum'' instead of ''row_number()'' is faster (it can use indexes), and doesn't require an ''order by'' clause when not required. The query would look like:
{{{
SELECT   ""ENTITY"".""ID"", ""ENTITY"".""NAME""
FROM     ""ENTITY""
WHERE    ROWNUM > 0 AND ROWNUM <= 10
ORDER BY ""ENTITY"".""ID""
}}}
It won't make a noticeable difference with tables with a couple of rows; but when you are reaching the million rows, you go from minutes to milliseconds."		closed	Database layer (models, ORM)	1.0		fixed			Unreviewed	1	0	0	0	0	0