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 Server / MS Access: ALTERTABLEPersons ALTERCOLUMNAge intNOTNULL; My SQL / Oracle (prior version 10G): ALTERTABLEPersons MODIFYCOLUMNAge intNOTNULL; Oracle 10G and later: ALTERTABLEPersons MODIFYAge intNOTNULL; Exercise? What is the purpose of the SQLNOT NULLconstraint?
SQL>alter table tt add constraint tt_con_c check(table_type is not null); Table altered. 表达的意思一样,都是设定table_type不可以为Null 但是查看constraint数据字典是,发现search condition显示的是小写的table_type is not null,和上一行的not null constraint有一些不一样。 SQL> select constraint_name...
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...
oracle约束总结(not null/unique/primary key/foreign key/check),约束(constraint):对创建的表的列属性、字段进行的限制。诸如:notnull/unique/primarykey/foreignkey/check作用范围:①列级约束仅仅能作用在一个列上②表级约束能够作用在多个列上(当然表级约束也能
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,
"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), ...
CREATETABLE"T_LDIM_AGENT_UPREL"("REL_AGENT_ID"NUMBER(22)CONSTRAINT"T_LDIM_AGENT_UPREL_OBNOTNULL_1679987669730612"NOTNULLENABLE,"AGENT_ID"NUMBER(22),"EMPLOYEE_ID"NUMBER(22),"EMP_PARTY_FULLNAME"VARCHAR2(60),"GRP_ID"NUMBER(22),"GRP_PARTY_FULLNAME"VARCHAR2(255),"CS_ID"NUMBER(22),"CS...
NOT IN 和 <>ALL 对 NULL 值敏感,这意味着 NOT IN 后面的子查询或者常量集合一旦有 NULL 值出现,则整个 SQL 的执行结果就会为 NULL。 所以一旦相关的连接列上出现了 NULL 值(实际只会判断字段是否有 NOT NULL 约束),此时 Oracle 如果还按照通常的 ANTI JOIN 的处理逻辑来处理(实际和 INNER JOIN 的处理逻...