mysql字段相关操作

alter table user add COLUMN new1 VARCHAR(20) DEFAULT NULL; //增加一个字段，默认为空
alter table user add COLUMN new2 VARCHAR(20) NOT NULL;  //增加一个字段，默认不能为空

alter table user DROP COLUMN new2; 　 //删除一个字段

alter table user MODIFY new1 VARCHAR(10); 　//修改一个字段的类型

alter table user CHANGE oldname newname int;　 //修改一个字段的名称，此时一定要重新指定该字段的类型

select COLUMN_NAME,column_comment,COLUMN_TYPE  from INFORMATION_SCHEMA.Columns
where table_name='表名' and table_schema='数据库名'

ALTER TABLE `school` ADD COLUMN `isDelete` int(1) DEFAULT 0 COMMENT '删除标识' AFTER `schoolNum`;
alter table school MODIFY isDelete int(2) DEFAULT 0 COMMENT '删除标识';
alter table school CHANGE isDelete myDelete int(2) DEFAULT 0 COMMENT '删除标识';
alter table school DROP COLUMN myDelete;
select * from school;

select COLUMN_NAME,column_comment,COLUMN_TYPE from INFORMATION_SCHEMA.Columns where table_name='school' and table_schema='my_demo20'