>> DB.select(:a.as(:x)).from(:test).first ~ SELECT a AS x FROM test LIMIT 1 => {:a=>"1"}

The problem is in process_result_set() in jdbc.rb

Starting with MySQL Connector/J 5.1 you will always get the real column name with getColumnName(). You should use getColumnLabel() instead which will return the alias if one has been specified, otherwise the name.

This is supposedly the correct JDBC behaviour. See for example: http://bugs.mysql.com/bug.php?id=31499

I've also (quickly) tested this patch with Oracle JDBC 10.2.0.4 and it seems to work fine.

Your analysis and patch appear to be correct, so applied: http://github.com/jeremyevans/sequel/commit/3b65291fd266d721bba3cb4d4630cfab0f4c11a0.

I also added an integration test, it passes on PostgreSQL, MySQL, SQLite, and H2 using the JDBC adapter (http://github.com/jeremyevans/sequel/commit/b15b96bb09c915032da19004c2ebb60dfbe952b5).

Thank you for finding and fixing this.