1、SQL Constraint Integrity Constraints are used to apply business rules for the database tables. The constraints available in SQL are Foreign Key, Not Null, Unique, Check. Constraints can be defined in two ways
Learn more about the Microsoft.SqlServer.Management.SqlParser.SqlCodeDom.SqlInlineIndexConstraint.Microsoft.SqlServer.Management.SqlParser.SqlCodeDom.ISqlTableElement.AsColumnDefinition in the Microsoft.SqlServer.Management.SqlParser...
CONSTRAINTPRIMARYKEY(id)-- 创建主键索引-- CONSTRAINT pk_name PRIMARY KEY(id) -- 创建自定义主键名称索引-- PRIMARY KEY(id,name) -- 创建联合索引,可以省略 constraint 语句);-- 使用 UNION 创建唯一索引CREATETABLEt2(
ALTER TABLE HumanResources.EmployeeDepartmentHistory CHECK CONSTRAINT FK_EmployeeDepartmentHistory_Department_DepartmentID; GO H. 重新生成已分区索引 下面的示例在 5 数据库中重新生成一个分区索引为 IX_TransactionHistory_TransactionDate 的分区,分区号为 AdventureWorks2022。 分区 5 是使用 ONLINE=ON 重新生成的...
1)唯一约束:uk_表名称_字段名。uk是UNIQUE KEY的缩写。比如给一个部门的部门名称加上唯一约束,来保证不重名,如下:ALTER TABLE t_dept ADD CONSTRAINT un_name UNIQUE(name)。 2)外键约束:fk_表名,后面紧跟该外键所在的表名和对应的主表名(不含t_)。子表名和父表名用下划线(_)分隔。如下:ALTER TABLE t...
,CONSTRAINT emp_email_uk UNIQUE (email) ... ); Theemp_email_uk constraint ensures that no two employees have the same emailaddress, as shown in Example5-1. Example 5-1 Unique Constraint SQL> SELECT employee_id, last_name,email FROM employees WHERE email = 'PFAY'; ...
该DROP INDEX语句不适用于通过定义PRIMARY KEY或UNIQUE约束创建的索引。 若要删除约束和相应的索引,请使用ALTER TABLE和DROP CONSTRAINT子句。 重要 将在SQL Server 的未来版本中删除定义的<drop_backward_compatible_index>语法。 请避免在新的开发工作中使用该功能,并考虑修改当前使用该功能的应用程序。 请改用在<dro...
Can't be created as a constraint-based index. It's possible to have unique constraints, primary key constraints, and foreign key constraints on a table with a columnstore index. Constraints are always enforced with a row-store index. Constraints can't be enforced with a columnstore (clustered...
When you create a PRIMARY KEY constraint, a unique index on the column, or columns, is automatically created. By default, this index is clustered; however, you can specify a nonclustered index when you create the constraint. Can be used in range queries.If...
The PRIMARY KEY constraint in the user table can't be modified while a spatial index is defined on a column of that table. To change the PRIMARY KEY constraint, first drop every spatial index of the table. After modifying the PRIMARY KEY constraint, you can re-create each of the spatial...