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 The constraints can be specified immediately after the column definition. This is ca...
Learn more about the Microsoft.SqlServer.Management.SqlParser.SqlCodeDom.SqlInlineIndexConstraint.Microsoft.SqlServer.Management.SqlParser.SqlCodeDom.ISqlTableElement.AsConstraint in the Microsoft.SqlServer.Management.SqlParser.SqlCodeDom na...
CONSTRAINT是一个子句，定义表结构时经常使用。例如：CONSTRAINT PK_EMP PRIMARY KEY(Empno)是设置主键，主键名字是PK_EMP。这时[index]由pk_emp替代了。严格的说constraint[index] 应该写成[constraint indexname]表示该子句可以省略。例如： PRIMARY KEY（empno）...
foreign key也有两个作用,一是约束作用(constraint),规范数据的引用完整性,但同时也在这个key上建立了一个index; 可见,mysql的key是同时具有constraint和index的意义,这点和其他数据库表现的可能有区别。 (至少在Oracle上建立外键,不会自动建立index),因此创建key也有如下几种方式: (1)在字段级以key方式建立, 如 ...
SORT_IN_TEMPDB MAXDOP DATA_COMPRESSION 注释 有关索引选项的完整说明,请参阅 CREATE INDEX (Transact-SQL)。 请参阅 参考 ALTER TABLE (Transact-SQL) column_constraint (Transact-SQL) computed_column_definition (Transact-SQL) table_constraint (Transact-SQL) 中文...
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...
Notice that none of the rows from the Production.UnitMeasure table were inserted into the table even though only one row in the table violated the UNIQUE index constraint. E. Using DROP_EXISTING to drop and re-create an index The following example drops and re-creates an existing index on ...
,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'; ...
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 AdventureWorks2022 数据库中重新生成一个分区索引为 5 的分区,分区号为 IX_TransactionHistory_TransactionDate。 分区 5 是使用 ONLINE=ON 重新生成的,并...
ALTER TABLE DROP CONSTRAINT (PRIMARY KEY or UNIQUE) Clustered index The underlying table cannot be modified, truncated, or dropped while an online index operation is in process. The online option setting (ON or OFF) specified when you create or drop a clustered index is applied to any nonclus...