select 10 rows per day with order

Question

i have a db with records with date (timestamp) i need to select 10 records for each day (there are many more per day) and order them by few columns...

how should that qu

Answer 1

After looking at (the ever excellent) xaprb blog from Baron Schwarz, http://www.xaprb.com/blog/2006/12/02/how-to-number-rows-in-mysql/ I wonder if the use of user-defined variables could work here.

select hiredate, ename, sal
from ( select hiredate, ename, sal,
       @num := if(@hiredate = hiredate, @num + 1, 1) as row_number,
       @hiredate := hiredate as dummy
     from emp_temp
) as x
where row_number < 3
order by hiredate, ename, sal

I've only tried the above for small sets of data, but it seems to work in bringing back just two records per hiredate. So far as I can tell from limited testing it should scale up for greater data sets. ( there may be performance issues in large data sets as Mysql is creating a temporary table)