PRIMARY KEY 或 UNIQUE 约束 在创建 PRIMARY KEY 约束时,如果不存在该表的聚集索引且未指定唯一非聚集索引,则将自动对一列或多列创建唯一聚集索引。 主键列不允许空值。 在创建 UNIQUE 约束时,默认情况下将创建唯一非聚集索引,以便强制 UNIQUE 约束。 如果不存在该表的聚集索引,则可以指定唯一聚集索引。
UNIQUE DESC ON UNPIVOT DISK OPEN UPDATE DISTINCT OPENDATASOURCE UPDATETEXT DISTRIBUTED OPENQUERY USE DOUBLE OPENROWSET USER DROP OPENXML VALUES DUMP OPTION VARYING ELSE OR VIEW END ORDER WAITFOR ERRLVL OUTER WHEN ESCAPE OVER WHERE EXCEPT PERCENT ...
2.1 创建数据库 CREATEDATABASEUserManagement;GOUSEUserManagement;GO 1. 2. 3. 4. 2.2 创建Users表 我们将创建一个Users表,并添加 CHECK 约束以满足我们的需求。 CREATETABLEUsers(UserIDINTPRIMARYKEYIDENTITY(1,1),EmailVARCHAR(255)UNIQUENOTNULL,AgeINTNOTNULL,CHECK(Age>0ANDAge<150));GO 1. 2. 3. ...
此外,CREATE TABLE 和ALTER TABLE 语句可用于设置 PRIMARY KEY 和UNIQUE 约束上的锁定粒度。 对于后向兼容,还可以使用 sp_indexoption 系统存储过程设置粒度。 若要显示给定索引的当前锁定选项,请使用 INDEXPROPERTY 函数。 可以禁止将页级锁、行级锁或页级锁和行级锁都用于指定的索引。 展开表 禁止的锁访问索引...
Can I have a primary key as a non-unique column Can I pass parameter to an ALTER DATABASE command Can I prevent deadlock during concurrent delete Can I print to file using T- SQL Can I sort an SQL table? Can I sort row without order by clause Can I UPDATE, then INSERT if no rec...
For example, to remove theuser_infoUNIQUE constraint that we have created in the example above, we use the following command: ALTERTABLEusersDROPCONSTRAINTuser_infoCode language:SQL (Structured Query Language)(sql) In this tutorial, we have shown you how to use SQL UNIQUE constraint to enforce...
Avoid using this syntax structure in new development work, and plan to modify applications that currently use the feature. Use the syntax structure specified in <relational_index_option> instead.syntaxsql Kopiera CREATE [ UNIQUE ] [ CLUSTERED | NONCLUSTERED ] INDEX index_name ON ( column_nam...
(this is an OFFLINE operation)-- Consider using bulk loading techniques to speed it upALTERTABLE[dbo].[latch_contention_table]ADD[HashValue]AS(CONVERT([tinyint],abs(binary_checksum([hash_col])%(16)),(0))) PERSISTEDNOTNULL;--Create the index on the new partitioning schemeCREAT...
In SQL Server, you use UNIQUE and CHECK constraints, which are database objects that enforce data integrity in SQL Server tables. To validate that a value is valid in another table, use a foreign key constraint. To validate that a value in a column is within a specific ...
Basic familiarity with executingSELECTqueries to select data from the database, as described in ourHow To SELECT Rows FROM Tables in SQLguide. Note:Please note that many RDBMSs use their own unique implementations of SQL. Although the commands outlined in this tutorial will work on most RDBMSs...