This week's book giveaway is in the OCMJEA forum. We're giving away four copies of OCM Java EE 6 Enterprise Architect Exam Guide and have Paul Allen & Joseph Bambara on-line! See this thread for details.
You'll need to execute an "ALTER TABLE" query. The exact syntax depends on the database server used, but in general it's something like this:
That last NULL indicates the column can have NULL values. Use "NOT NULL" instead to indicate it cannot have NULL values, but that's only possible if you have no rows yet, unless you specify a default value:
Final part of the lesson: you can also change existing columns, to change the type, allow/disallow NULL values or change the default: