alter table example modify id varchar(20); --7添加约束 -- foreign key alter table example add constraint fk_example_xxx foreign key(pid) references xxx(pid); insert into example(name,age) values('张三1',1); insert into example(name,age) values('张三2',2); insert into example(name,ag...
ALTER TABLE table_name MODIFY new_column DEFAULT 'example'; 1. 2. 如果你希望新字段不能为空,你可以使用ALTER TABLE语句的NOT NULL子句。例如,以下命令将"new_column"字段设为非空: ALTER TABLE table_name MODIFY new_column NOT NULL; 1. 2. 最后,你可以使用DESCRIBE命令来验证表结构是否已成功修改。例...
ALTER TABLE members ADD birth_date DATE NOT NULL; Code language: SQL (Structured Query Language) (sql) In this example, the birth_date column is a DATE column and it does not accept null. Suppose, you want to record the time at which a row is created and updated. To do so, you ne...
(1)约束是和表关联的,可在create table或alter table table_name add/drop/modify来建立、修改、删除约束。 可以临时禁止约束,如: alter table book_example disable constraint book_example_1; alter table book_example enable constraint book_example_1; (2)主键和外键被称为表约束,而not null和unique之类的...
ALTER TABLE employees ADD (email VARCHAR2(50) NOT NULL); 2、修改列 要修改表中的列,可以使用ALTER TABLE语句和MODIFY子句,语法如下: ALTER TABLE 表名 MODIFY (列名 新数据类型 [约束条件]); 将employees表中的salary列的数据类型从NUMBER(6,2)修改为NUMBER(8,2): ...
For example, to add addr, pin, ph, fax to employees table we will give the following command alter table emp add (addr varchar2(20), pin varchar2(10),ph varchar2(20)); How about adding columns with NOT NULL constraint As we have seen above, when we add a column, the column will...
http://dba-oracle.com/t_alter_table_modify_column_syntax_example.htm For complete tips on Oracle alter table syntax, see the book "Easy Oracle Jumpstart". Oracle provides "alter table" syntax to modify data columns in-place in this form: ...
For example, we try to shorten the size of thephonecolumn down to 12 characters: ALTERTABLEaccountsMODIFYphoneVARCHAR2(12);Code language:SQL (Structured Query Language)(sql) Oracle Database issued the following error: To fix this, first, we should remove the international code from the phone ...
SQL> alter user scott account unlock; SQL> alter user scott identified by tiger; 删除oracle用户: SQL>drop user username cascade; (删除与用户相关的所有对象) 这样该用户包括该用户下的表,试图,同义词,过程,索引,及相关的一切就删除了。 创建用户并赋权限以及设置默认表空间。
若数据库版本大于等于 12.2.0.1 时,在创建非 cdb 或包含至少一个 pdb 的 cdb 数据库时,会创建示例数据库,但是相关的示例数据位于 SYSAUX 表空间。若数据库版本小于 12.2.0.1 时,则示例数据位于 EXAMPLE 表空间。 12c 版本的 CDB 数据库不再包含示例数据库和示例表空间。