drop constraint var_name_fk; 或者 alter table table_name drop constraint add_name_nn; ---参考:[oracle添加notnull约束](http://www.2cto.com/database/201503/382810.html)
ALTER TABLE table_name DROP CONSTRAINT constraint_name 其具体使用参见第10章表的约束、索引与视图。★ 注意 ★使用ALTER TABLE修改表时要特别慎重,因为有些操作对数据库影响很大,且是不可逆的。如果用户采用DROP COLUMN关键字删除表中的某列,则该列所有已经存在的数据记录均被删除了。
If any omitted column has a NOT NULL constraint and no default value, then Oracle returns an error indicating that the constraint has been violated and rolls back the INSERT statement.If you omit the column list altogether, then the values_clause or query must specify values for all columns ...
If you omit one of the table's columns from this list, the column's value for the inserted row is the column's default value as specified when the table was created or last altered. If any of these columns has aNOTNULLconstraint, then Oracle returns an error indicating that the constrai...
MySQL / SQL Server / Oracle / MS Access: CREATE TABLE Persons ( Id_P int NOT NULL, LastName varchar(255) NOT NULL, FirstName varchar(255), Address varchar(255), City varchar(255),CONSTRAINTchk_PersonCHECK(Id_P>0ANDCity='Sandnes')) ...
It also has a not null constraint. And creates a unique index in the background.To create one, add the organization index clause to the table definition:Copy code snippet Copied to Clipboard Error: Could not Copy Copied to Clipboard Error: Could not Copy create table toys ( toy_name ...
create table 表名称(字段1 数据类型 not null unique,字段2 数据类型 约束) 或 alter table 表名称 add unique(字段1); 设置多个字段的唯一值 适用于MySQL / SQL Server / Oracle / MS Access: create table 表名称(字段1 数据类型 not null,字段2 数据类型 ,[constraint 自定义约束名称] unique(字段1,...
虽然西西不建议大家去用命令删除数据库表中的东西,但是这些删除命令总有用的着的地方。 说到删除表数据的关键字,大家记得最多的可能就是delete了 然而我们做数据库开发,读取数据库数据.对另外的两兄弟用得就比较少了 现在来介绍另外两个兄弟,都是删除表数据的,其实也是很容易理解的 ...
studio_id number not null, CONSTRAINT f_studio FOREIGN KEY(studio_id) REFERENCES studio (studio_id) ON DELETE CASCADE ); If we attempt to drop the table without removing the constraints, oracle returns an error as shown: DROP TABLE studio; ...
Modify, drop, and add constraints,ApsaraDB for OceanBase:This topic describes the conversion scope of constraint modification, dropping, and addition in ALTER TABLE DDL operations during data migration from an Oracle database to an Oracle tenant of Ocean