Oracle 增加 修改 删除 列

语法结构如下：alter table tablename add (column datatype [default value][null/not null],….);alter table tablename modify (column datatype [default value][null/not null],….);alter table tablename drop (column); 例子：增加列alter table t_jm_user add USR_EmailValidate CHAR(1) default 'N' not null; 修改列alter table t_jm_user modify USR_EmailValidate CHAR(1) default 'Y'  null; 删除列alter table t_jm_user drop column  USR_EmailValidate; 增加约束alter table user
  add constraint FK_user_CLIENT foreign key (COMP_ID)
  references T_stal (COMP_ID); 删除约束alter table user drop constraint FK_user_CLIENT ;