Often you’ll desire a little more control over how your selected data is retrieved. The two most common ways of organizing your data are to order the retrieved rows by one or more columns, or to group the retrieved rows and apply functions to the groups instead of to individual rows.
Perl is well-suited to these tasks within your program, but performing ordering and grouping via SQL will offload the task onto the database server and also will save you writing, or using, potentially suboptimal techniques for organizing the data. Therefore, generally, use SQL rather than your own application-level code.
Ordering the data retrieved by a SELECT statement
is easy and can be achieved simply by an
ORDER
BY clause. This
clause is always found at the end of your queries, after all the join
conditions have been specified.
The ORDER
BY clause is
specified as a comma-separated list of columns that should be used to
order the data. For example, an ORDER BY clause
of:
ORDER BY name, location
would order the rows by name and, if the names of the sites are
identical, the location column would be used as a secondary ordering.
You can change the direction of the ordering from the default
``ascending'' order (which goes from A to Z)
to a ``descending'' order by appending the
DESC
keyword
to any field names in the ORDER
BY clause.