Learn how to add a unique constraint to an SQL column using ALTER TABLE. Ensure data integrity and prevent duplicate entries with this step-by-step guide.
SQL> create table test6 as select object_id,object_name from dba_objects; Table created. SQL> create table test6u nologging as select * from test6; Table created. SQL> create unique index uni_test6 on test6(object_id); Index created. SQL> alter table test6u add constraint uni_test7 ...
ALTER TABLE 部门信息 ADD CONSTRAINT uk_dptname UNIQUE(部门名称) 1. **问题完整性判断**:题目提供了完整的 SQL 语法结构,包含表名(部门信息)、约束类型(UNIQUE)、约束名称(uk_dptname)和目标列(部门名称),语法格式符合标准 SQL 规范。2. **唯一约束的作用**:该语句的目的是为“部门名称”列添加唯一性约...
题目考查对SQL语句`ALTER TABLE`添加约束的理解。具体语句为: ```sql ALTER TABLE userinfo ADD CONSTRAINT uq_userid UNIQUE(userid) ``` 该语句的功能是向`userinfo`表的`userid`字段添加**唯一约束**,约束的名称是`uq_userid`。 对各选项逐一分析: - **A. userid 主键**:错误。`UNIQUE`表明添加的是...
Source: AddUniqueConstraintOperation.cs 用于MigrationOperation 添加新的唯一约束的 。 C# 复制 [System.Diagnostics.DebuggerDisplay("ALTER TABLE {Table} ADD CONSTRAINT {Name} UNIQUE")] public class AddUniqueConstraintOperation : Microsoft.EntityFrameworkCore.Migrations.Operations.MigrationOperation,...
UsingALTER PRIMARY KEYwould have created aUNIQUEsecondary index calledusers_city_id_key. Instead, there is just one index for the primary key constraint. See also
SQL Copy -- Add a primary key > CREATE TABLE persons(first_name STRING NOT NULL, last_name STRING NOT NULL, nickname STRING); > ALTER TABLE persons ADD CONSTRAINT persons_pk PRIMARY KEY(first_name, last_name); -- Add a foreign key which Databricks does not enforce, but c...
alter table userinfo add constraint uq_userid unique(userid) 执行成功后,为userinfo表的( )字段添加了( )约束。 A. Userid ; 主键 B. Userid ; 唯一 C. Uq_userid ;外键 D. Uq_userid ;检查 相关知识点: 试题来源: 解析 B. Userid ; 唯一 反馈...
Using a UNIQUE constraint: ALTER TABLE [dbo].[Department] ADD CONSTRAINT [IX_DepartmentID] UNIQUE ( [DepartmentID] ) GO ALTER TABLE [dbo].[Employee] ADD CONSTRAINT [FK_Employee_Department] FOREIGN KEY ( [DepartmentID] ) REFERENCES [dbo].[Department] ( [DepartmentID] ) ...
在创建外键之时,使用的SQL和碰到错误信息如下: alter table `product" add CONSTRAINT `sid_ref` FOREIGN KEY (`sid`) REFERENCES `sealer` (`id`) ON DELETE NO ACTION ON UPDATE NO ACTION 碰到的错误信息如下: 无法正确的插入外键约束。3、问题分析主外键更多的是某表的主键与子表的某个列进行关联,要求...