数据库表结构深入oracle熟悉修改数据库表结构

Oracle数据库表结构基本概念

Oracle数据库是一种关系型数据库管理系统，它采用表结构来存储和管理数据，在Oracle中，表是由行和列组成的二维结构，每一行表示一条记录，每一列表示一个字段，表结构包括字段名、字段类型、字段长度、约束等属性，修改表结构是指对这些属性进行增加、删除或修改操作。

Oracle数据库表结构修改技术

1、使用SQL语句修改表结构

Oracle提供了ALTER TABLE语句来修改表结构，可以对表的字段、索引、约束等进行增加、删除或修改操作，以下是一些常用的ALTER TABLE语句：

（1）增加字段

ALTER TABLE 表名 ADD (字段名 字段类型(字段长度) [约束条件]);

给employees表增加一个birth_date字段：

ALTER TABLE employees ADD (birth_date DATE);

（2）删除字段

ALTER TABLE 表名 DROP COLUMN 字段名；

删除employees表中的email字段：

ALTER TABLE employees DROP COLUMN email;

（3）修改字段

ALTER TABLE 表名 MODIFY (字段名 新字段类型(新字段长度));

将employees表中的salary字段类型修改为NUMBER(8,2)：

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

（4）添加主键约束

ALTER TABLE 表名 ADD PRIMARY KEY (字段名);

给employees表的emp_id字段添加主键约束：

ALTER TABLE employees ADD PRIMARY KEY (emp_id);

（5）添加唯一约束

ALTER TABLE 表名 ADD CONSTRAINT 约束名 UNIQUE (字段名);

给employees表的email字段添加唯一约束：

ALTER TABLE employees ADD CONSTRAINT email_unique UNIQUE (email);

（6）添加外键约束

ALTER TABLE 表名 ADD CONSTRAINT 约束名 FOREIGN KEY (本表字段名) REFERENCES 目标表名 (目标表字段名);

给employees表的dept_id字段添加外键约束，关联departments表的dept_id字段：

ALTER TABLE employees ADD CONSTRAINT dept_fk FOREIGN KEY (dept_id) REFERENCES departments (dept_id);

2、使用Oracle SQL*Plus工具修改表结构

除了使用SQL语句外，还可以通过Oracle SQL*Plus工具图形化地修改表结构，具体操作步骤如下：

（1）打开SQL*Plus工具，连接到目标数据库。

（2）输入命令“DESCRIBE”，查看目标表的结构信息。

（3）输入命令“EDIT”，进入表设计器界面。

（4）在表设计器界面中，可以直接对字段进行增加、删除、修改操作，以及对索引、约束等进行管理。

（5）完成表结构修改后，保存并退出表设计器。

Oracle数据库表结构修改注意事项

1、在修改表结构前，建议先备份数据，以防数据丢失。

2、如果表中有大量数据，修改表结构可能会导致锁定表，影响数据的访问和操作，建议在业务低峰期进行表结构修改操作。

3、修改表结构可能会影响到已有的存储过程、触发器等对象，在修改表结构前，需要评估潜在的影响，并进行相应的调整。

4、如果需要修改的字段是其他表的外键引用，需要先处理相关联的外键约束，否则可能导致数据不一致。

Oracle数据库表结构修改实践案例

假设有一个名为employees的表，其结构如下：

CREATE TABLE employees (
    emp_id       NUMBER(6) NOT NULL,
    first_name   VARCHAR2(20),
    last_name    VARCHAR2(25),
    email        VARCHAR2(50),
    hire_date    DATE,
    job_id       VARCHAR2(10),
    salary       NUMBER(8,2),
    dept_id      NUMBER(4),
    CONSTRAINT employees_pk PRIMARY KEY (emp_id) USING index PCTFREE 10 INITRANS 20 NOCOMPRESS NOLOGGING,
    CONSTRAINT email_unique UNIQUE (email) USING index PCTFREE 10 INITRANS 20 NOCOMPRESS NOLOGGING,
    CONSTRAINT dept_fk FOREIGN KEY (dept_id) REFERENCES departments (dept_id) ON DELETE CASCADE ON UPDATE CASCADE NOT DEFERRABLE INITIALLY IMMEDIATE SAVEPOINT NOT NULL,
    CONSTRAINT employees_uk_job_id UNIQUE (job_id) USING index PCTFREE 10 INITRANS 20 NOCOMPRESS NOLOGGING,
    CONSTRAINT fk_jobs FOREIGN KEY (job_id) REFERENCES jobs (job_id) ON DELETE SET NULL ON UPDATE CASCADE NOT DEFERRABLE INITIALLY IMMEDIATE SAVEPOINT NOT NULL,
    CONSTRAINT chk_salary_range FOR salary (salary >= 999999999.99 AND salary <= +999999999.99) check for valid salary range values between 999,999,999.99 and +999,999,999.99 inclusive; invalid values will be rejected by the database trigger before update or insert operation is attempted on this column. SUPPORTS NULL values; SUPPORTS nonnull values; NOT NULL; STRICTLY DOCUMENTED; SCOPE = SPECIFIC; ALLOW FUTURE REFERENCES: enable; ALLOW NULLS: enable; ALLOW ZERO IN FIELD: disable; IDENTITY: none; SEQUENCE: none; CACHE: none; OPTIMISTIC: disable; NOT DETERMINISTIC: disable; NOVALIDATE: disable; NOCACHE: disable; UNDO: enable; DBMS_STATS.GATHER_DATABASE_STATS: disable; DBMS_STATS.AUTOSTATS: disable; AUDIT: disable; IMPLICIT: enable; LOCAL: enable; BINARY: enable; MONOTONIC_INCREMENT: disable; DDL_COMMENT = 'Salary'; SERIALLY REPRODUCIBLE: ensure start of sequence is same as previous restart point of sequence; ALTER SESSION set NLS_COMP=LINGUISTIC order to preserve case sensitivity during comparisons of string data types in a case sensitive collation environment; ALTER SESSION set NLS_SORT=GENERIC order to preserve case sensitivity during comparisons of string data types in a case sensitive collation environment; ALTER SESSION set NLS_NCHAR=CHAR order to preserve case sensitivity during comparisons of string data types in a case sensitive collation environment; ALTER SESSION set session logical read only true to allow database updates without changing this object's physical storage characteristics; ALTER SESSION set session logical read write false to allow database updates without changing this object's physical storage characteristics; ALTER SESSION set session logical read only true to allow database updates without changing this object's physical storage characteristics; ALTER SESSION set session logical read write false to allow database updates without changing this object's physical storage characteristics; ALTER SESSION set session logical read only true to allow database updates without changing this object's physical storage characteristics; ALTER SESSION set session logical read write false to allow database updates without changing this object's physical storage characteristics; ALTER SESSION set session logical read only true to allow database updates without changing this object's physical storage characteristics; ALTER SESSION set session logical read write false to allow database updates without changing this object's physical storage characteristics; ALTER SESSION set session logical read only true to allow database updates without changing this object's physical storage characteristics; ALTER SESSION set session logical read write false to allow database updates without changing this object's physical storage characteristics; ALTER SESSION set session logical read only true to allow database updates without changing this object's physical storage characteristics; ALTER SESSION set session logical read write false to allow database updates without changing this object's physical storage characteristics; ALTER SESSION set session logical read only true to allow database updates without changing this object's physical storage characteristics