Oracle中的DDL(Data Definition Language)语句用于定义和管理数据库中的对象,包括表、索引、视图等,下面是关于Oracle中DDL语句的详细用法:
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1、创建表(CREATE TABLE)
语法:
```sql
CREATE TABLE table_name (
column1 datatype [constraints],
column2 datatype [constraints],
...
);
```
示例:
```sql
CREATE TABLE employees (
id NUMBER(6) PRIMARY KEY,
name VARCHAR2(50),
age NUMBER(3),
salary NUMBER(8, 2)
);
```
2、修改表结构(ALTER TABLE)
语法:
```sql
ALTER TABLE table_name
ADD column_name datatype [constraints];
ALTER TABLE table_name
DROP COLUMN column_name;
ALTER TABLE table_name
MODIFY column_name datatype;
```
示例:
```sql
ALTER TABLE employees
ADD email VARCHAR2(100);
ALTER TABLE employees
DROP COLUMN age;
ALTER TABLE employees
MODIFY name VARCHAR2(75);
```
3、删除表(DROP TABLE)
语法:
```sql
DROP TABLE table_name;
```
示例:
```sql
DROP TABLE employees;
```
4、创建索引(CREATE INDEX)
语法:
```sql
CREATE [UNIQUE] [CLUSTER] INDEX index_name ON table_name (column1, column2, ...);
```
示例:
```sql
CREATE INDEX idx_employees_name ON employees (name);
```
5、删除索引(DROP INDEX)
语法:
```sql
DROP INDEX index_name;
```
示例:
```sql
DROP INDEX idx_employees_name;
```
6、创建视图(CREATE VIEW)
语法:
```sql
CREATE [OR REPLACE] [FORCE] [NO FORCE] VIEW view_name AS select_statement;
```
示例:
```sql
CREATE OR REPLACE VIEW employees_over_30 AS
SELECT * FROM employees WHERE age > 30;
```
7、删除视图(DROP VIEW)
语法:
```sql
DROP [RECYCLE] [PURGE] view_name;
```
示例:
```sql
DROP view employees_over_30;
```