How to select top N from a table

Question

I have to select the top 25 records from a table according to the column Num.

There are two issues. First, the table is not sorted by Num.

Answer 1

It depends heavily on your database, as there is no standard way to do this.

In SQL Server, for example, I have used Row_Number (http://msdn.microsoft.com/en-us/library/ms186734.aspx) to do this, so I can select which group I was interested in (for paging, for example), but Top also works.

For Oracle you can look at rownum (http://www.adp-gmbh.ch/ora/sql/examples/first_rows.html).

And MySQL has been mentioned already.