code: public boolean changeColumn (Connection conn, String table, String column, String type,
                                   Boolean nullable, Boolean unique, String defaultValue)
          throws SQLException
      {
          String defStr = expandDefinition(type, nullable != null ? nullable : false,
                                           unique != null ? unique : false, defaultValue);
  
          executeQuery(conn, "ALTER TABLE " + tableSQL(table) + " CHANGE " +
                       columnSQL(column) + " " + columnSQL(column) + " " + defStr);
          log("Database column '" + column + "' of table '" + table + "' modified to have " +
              "definition '" + defStr + "'.");
          return true;
      }
docs: from DatabaseLiaison