所以SQL Server的唯一键和唯一索引会将空值(NULL)也算作重复值,我们可以将上面的唯一键IX_UniqueStudentCode删掉,将其建立为唯一索引: ALTERTABLE[dbo].[Students]DROPCONSTRAINT[IX_UniqueStudentCode]CREATEUNIQUENONCLUSTEREDINDEX[IX_UniqueStudentCode]ON[
1.设置表的联合主键 2.在INSERT语句中添加OR IGNORE,即可(重复数据会跳过,且不影响后续数据插入) 示例如下: insert OR IGNORE into PDA_Test (DeviceID,MethodName) values('1112','测试原有'); sqlite避免重复插入数据。 SQLite 数据库常用约束如下: NOT NULL - 非空 UNIQUE - 唯一 PRIMARY KEY - 主键 FO...
当决定是否创建一个唯一约束或者仅仅只是创建一个唯一索引时,请遵从MSDN库中的SQL SERVER文档: “There are no significant differences between creating a UNIQUE constraint and creating a unique index that is independent of a constraint. Data validation occurs in the same manner, and the query optimizer d...
ALTER TABLE uniqueTest NOCHECK CONSTRAINT ALL; DELETE FROM uniqueTest WHERE id IS NULL; INSERT INTO uniqueTest VALUES(NULL); GO 2 1. 2. 3. 4. 5. 虽然禁用了表上的所有约束,但重复键NULL仍然不能插入列中。 然而,当我启用约束,禁用唯一约束创建的索引时,发现可以插入重复值了。 --起用所有约束 A...
public abstract class SqlUniqueConstraintBase : Microsoft.SqlServer.Management.SqlParser.SqlCodeDom.SqlConstraint, Microsoft.SqlServer.Management.SqlParser.SqlCodeDom.ISqlTableElementInheritance Object SqlCodeObject SqlConstraint SqlUniqueConstraintBase Derived...
CREATETYPEdbo.udt_moneyFROMvarchar(11)NOTNULL; GOGRANTREFERENCESONTYPE::dbo.udt_moneyTOpublic 如果执行此操作,则此数据类型和REFERENCES权限将永久可用tempdb。 否则,当 SQL Server 重新启动时,用户定义的数据类型和权限将消失。 有关详细信息,请参阅CREATE TABLE。
Applies to: SQL Server 2016 (13.x) and later versions Azure SQL Database Azure SQL Managed Instance SQL database in Microsoft Fabric You can create a unique constraint in SQL Server by using SQL Server Management Studio or Transact-SQL to ensure no duplicate values are entered in specific ...
UNIQUE constraints Constraints are rules that the SQL Server Database Engine enforces for you. For example, you can useUNIQUEconstraints to make sure that no duplicate values are entered in specific columns that don't participate in a primary key. Although both aUNIQUEconstraint and aPRIMARY KEY...
You can create a unique constraint in SQL Server by using SQL Server Management Studio or Transact-SQL to ensure no duplicate values are entered in specific columns that don't participate in a primary key. Creating a unique constraint automatically creates a corresponding unique index. Note For ...
违反了唯一性约束，所以导致插入不正确。ORACLE违反唯一约束条件解决方法 java代码报错：java.sql.BatchUpdateException: ORA-00001: 违反唯一约束条件 (TTT.table)at oracle.jdbc.driver.DatabaseError.throwBatchUpdateException(DatabaseError.java:629)at oracle.jdbc.driver.OraclePreparedStatement.executeBatch(...