修改表和约束

（一）修改表列

语法：alter table [schema_name.]table_name

{

　　add column_name data_type [column_attributes] |

　　drop column column_name |

　　modify column_name data_type [column_attributes]

}

1 新增表列

alter table invoice_check add invoice_name varchar2(200);

2 修改表列

alter table invoice_check MODIFY invoice_name varchar2(100) CHECK(LENGTH(invoice_name) <= 50);

3 删除表列

alter table invoice_check DROP COLUMN invoice_name;

4 重命名表列

alter table invoice_check RENAME COLUMN invoice_name TO invoice_name_short;

(二） 修改约束

语法：alter table table_name

{

　　add constraint constraint_name constraint_definition [DISABLE] |

　　drop constraint constraint_name　　|

　　enable [novalidate] constraint_name 　　|

　　DISABLE　　constraint_name

}

1 添加约束

alter table invoice_check ADD CONSTRAINT invoice_check_pk PRIMARY KEY (invoice_id);

2 删除约束

alter table invoice_check DROP CONSTRAINT invoice_check_pk;

3 启用/ 禁用 约束

alter table invoice_check ENABLE CONSTRAINT invoice_check_pk;

alter table invoice_check DISABLE CONSTRAINT invoice_check_pk;