1. 新增一個欄位
ALTER TABLE `{<em>table_name</em>}` ADD `{<em>new_column_name</em>}` {new_column_type} CHARACTER SET utf8 COLLATE utf8_general_ci NOT NULL ;

EX:
ALTER TABLE `User` ADD `name` VARCHAR( 50 ) CHARACTER SET utf8 COLLATE utf8_general_ci NOT NULL ;

EX:
ALTER TABLE `User` ADD `name` VARCHAR( 50 ) CHARACTER SET utf8 COLLATE utf8_general_ci NOT NULL default '' COMMENT '姓名' ;

2. 修改已經存在的欄位
ALTER TABLE `{<em>table_name</em>}` CHANGE `{<em>column_name_original</em>}` `{<em>column_name_modified</em>}` {<em>column_type</em>} CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT '{<em>default_value</em>}'

EX:
ALTER TABLE `User` CHANGE `name` `name` VARCHAR( 50 ) CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT ' '