oracle 修改表结构语句

oracle 修改表结构语句
Oracle中可以使用ALTER TABLE语句来修改表的结构。

添加列：

ALTER TABLE table_name ADD column_name data_type;

示例：ALTER TABLE employees ADD email VARCHAR2(50);

删除列：

ALTER TABLE table_name DROP COLUMN column_name;

示例：ALTER TABLE employees DROP COLUMN email;

修改列名称及数据类型：

ALTER TABLE table_name RENAME COLUMN old_column TO new_column;

ALTER TABLE table_name MODIFY (old_column new_data_type);

示例：ALTER TABLE employees RENAME COLUMN salary TO monthly_salary;

ALTER TABLE employees MODIFY (monthly_salary NUMBER(8,2));

修改列默认值：

ALTER TABLE table_name MODIFY column_name DEFAULT default_value;

示例：ALTER TABLE employees MODIFY (email DEFAULT 'example@gmail.com');

修改主键或外键约束：

ALTER TABLE table_name ADD CONSTRAINT constraint_name PRIMARY KEY (column_list) USING INDEX index_name;

ALTER TABLE table_name ADD CONSTRAINT constraint_name FOREIGN KEY (column_list) REFERENCES referenced_table (referenced_columns);

示例：ALTER TABLE orders ADD CONSTRAINT pk_orders PRIMARY KEY (order_id) USING INDEX idx_pk_orders;

ALTER TABLE order_items ADD CONSTRAINT fk_order_items FOREIGN KEY (order_id) REFERENCES orders (order_id);