alter table tt modify(table_type varchar2(11) constraint tt_con_nn not null); 查看数据字典。 SQL> select column_name ,nullable from user_tab_cols where table_name='TT'; COLUMN_NAME NUL --- --- TABLE_NAME N TABLE_TYPE N SQL> select constraint_name,constraint_type,search_condition from...
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): ...
——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...
Here, the SQL command adds theNOT NULLconstraint to thecollege_idcolumn in the existingCollegestable. Error Due to NOT NULL Constraint We must enter a value into columns with theNOT NULLconstraint. Otherwise, SQL will give us an error. For example, thecollege_idcolumn of ourCollegestable has...
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...
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,
使用外键将数据插入表中的T-SQL 、、 我正在使用Server 2014来创建数据并将数据插入到表中,在使用外键约束填充表时出现了一个问题。我有一个表user和一个表city,它们都是预先创建的。我使用代码修改user表以包含表city中的cityId外键,其中包含以下代码: ADD cityId UNIQUEIDENTIFIER NOT NULL CONSTRAINT usr_ ...
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 ...
"REL_AGENT_ID" NUMBER(22) CONSTRAINT "T_LDIM_AGENT_UPREL_OBNOTNULL_1679987669730612" NOT NULL ENABLE, "AGENT_ID" NUMBER(22), "EMPLOYEE_ID" NUMBER(22), "EMP_PARTY_FULLNAME" VARCHAR2(60), "GRP_ID" NUMBER(22), "GRP_PARTY_FULLNAME" VARCHAR2(255), ...
create table member (mid number,name varchar2(20) CONSTRAINT nn_name NOT NULL ,email varchar2(30) CONSTRAINT uk_email unique );