Sort NULL values to the end of a table

NULL values are sorted last in default ascending order. You don't have to do anything extra.

The issue applies to descending order, which is the perfect inverse and thus sorts NULL values on top.
PostgreSQL 8.3 introduced NULLS LAST:

ORDER BY somevalue DESC NULLS LAST

For PostgreSQL 8.2 and older or other RDBMS without this standard SQL feature:

ORDER BY (somevalue IS NULL), somevalue DESC

FALSE sorts before TRUE, so NULL values come last, just like in the example above.

See:

• Sort by column ASC, but NULL values first?
• The manual on SELECT

Does this make the trick?

ORDER BY somevalue DESC NULLS LAST

Taken from: http://www.postgresql.org/docs/9.0/static/sql-select.html