oracle的constraint有6类,如下。 但是基于列的constraint主要有 type 为C,P,R,U 接触比较多的。 今天来和大家讨论check constraint和not null constraint,它们的constraint type都为C,但是实际应用中还是有很大的差别。 有一天开发人员反馈,说有一个表的某个字段有问题,标记为not null的,但是通过desc来查看的时候,...
——ON DELETE SET NULL(级联置空): 子表中对应的列置空 constraint emp1_dept_id_fkforeign key(dept_id)referencesdepartments(department_id)ON DELETE CASCADE 1. ——CHECK :定义每一行必须满足的条件 ..., salary NUMBER(2) CONSTRAINT emp_salary_min CHECK (salary > 0),... 1. 2. 3. 1.怎样...
An OracleNOT NULLconstraint specifies that a column cannot containNULLvalues. The OracleNOT NULLconstraints are inline constraints which are typically used in the column definition of theCREATE TABLEstatement. CREATETABLEtable_name ( ... column_name data_typeNOTNULL... );Code language:SQL (Structur...
SQL NOT NULL on ALTER TABLE To create aNOT NULLconstraint on the "Age" column when the "Persons" table is already created, use the following SQL: SQL Server / MS Access: ALTERTABLEPersons ALTERCOLUMNAge intNOTNULL; My SQL / Oracle (prior version 10G): ...
1. 数据库有六大约束 主键(primary key) 外键(foreign key):被参照的键必须有唯一约束或是主键 非空(not null) 默认(default) 检查(check):oracle独有 唯一(unique) 2. 六大约束的用法 以下所有演示的SQL语句都是基于Oracle,
ALTER TABLE student ADD CONSTRAINT chk_gender CHECK (gender in ('男', '女')); 4. Oracle中五种常见的约束类型: Oracle数据库提供了五种常见的约束类型,用于确保不同场景下数据的完整性: NOT NULL约束:用于确保某列不能为空。例如,在dept表中,列deptno定义为NOT NULL,插入或更新数据时,必须为该列提供...
Oracle中的Null(再提) NULL in Oracle A column in a table can be defined with the not null constraint. See also NULLs and boolean operators nvl, nvl2 and lnnvl are SQL constructs that are related to NULL handling. The ...
NOT NULL Constraint With Alter Table We can also add theNOT NULLconstraint to a column in an existing table using theALTER TABLEcommand. For example, SQL Server ALTERTABLECollegesALTERCOLUMNcollege_idINTNOTNULL; Oracle ALTERTABLECollegesMODIFYcollege_idINTNOTNULL; ...
1回答 填充外键字段时出现NOT NULL约束失败错误 、、、 我正在尝试运行我编写的脚本,将一些数据从json文件移动到我的数据库中,但仍然得到相同的错误。328, in executesqlite3.IntegrityError: NOT NULL我也已经在模型的外键字段中设置了null=True和blank=True:models.py # ...
create table member (mid number,name varchar2(20) CONSTRAINT nn_name NOT NULL ,email varchar2(30) CONSTRAINT uk_email unique );