oracle alter语句的用法是什么

1. 添加列：ALTER TABLE table_name ADD column_name data_type;

2. 修改列的数据类型：ALTER TABLE table_name MODIFY column_name new_data_type;

3. 修改列的名称：ALTER TABLE table_name RENAME COLUMN old_column_name TO new_column_name;

4. 删除列：ALTER TABLE table_name DROP COLUMN column_name;

5. 添加主键约束：ALTER TABLE table_name ADD CONSTRAINT constraint_name PRIMARY KEY (column_name);

6. 添加外键约束：ALTER TABLE table_name ADD CONSTRAINT constraint_name FOREIGN KEY (column_name) REFERENCES other_table (other_column);

7. 添加索引：CREATE INDEX index_name ON table_name (column_name);

8. 删除索引：DROP INDEX index_name;

总而言之，ALTER语句允许用户对数据库表进行更改，以满足不同的需求和要求。