UNIQUE(ID) ); To name aUNIQUEconstraint, and to define aUNIQUEconstraint on multiple columns, use the following SQL syntax: MySQL / SQL Server / Oracle / MS Access: CREATETABLEPersons ( ID intNOTNULL, LastName varchar(255)NOTNULL,
Here, the SQL command adds theUNIQUEconstraint to thecolleges_idcolumn in the existingCollegestable. For Multiple Columns -- add unique constraint to multiple columnsALTERTABLECollegesADDUNIQUEUnique_College (college_id, college_code); Here, the SQL command adds theUNIQUEconstraint tocollege_idandcoll...
The UNIQUE constraint uniquely identifies each record in a database table. The UNIQUE and PRIMARY KEY constraints both provide a guarantee for uniqueness for a column or set of columns. A PRIMARY KEY constraint automatically has a UNIQUE constraint defined on it. Note that you can have many UNI...
CONSTRAINT [FK_Sale_MerchInfo] FOREIGN KEY ( [MerChID] ) REFERENCES MerchInfo ( [MerchID] ) ON DELETE CASCADE GO /*入库表中商品编号与商品信息表之间的外键约束*/ ALTER TABLE Stock ADD CONSTRAINT [FK_Stock_MerchInfo] FOREIGN KEY ( [MerchID] ) REFERENCES MerchInfo ( oershi...
USEAdventureWorks2022; GOCREATETABLEProduction.TransactionHistoryArchive2 ( TransactionIDintNOTNULL,CONSTRAINTAK_TransactionIDUNIQUE(TransactionID) ); GO 在可为空的列上创建唯一约束 在“对象资源管理器”中,连接到 数据库引擎的实例。 在“标准”栏上,选择“新建查询”。
试着做这样的事情：
USEAdventureWorks2022; GOCREATETABLEProduction.TransactionHistoryArchive4 ( TransactionIDintNOTNULL,CONSTRAINTAK_TransactionIDUNIQUE(TransactionID) ); GO 在現有的資料表上建立 Unique 條件約束 在物件總管中,連線到資料庫引擎的執行個體。 在[標準]列上,選取 [新增查詢]。
在SQLAlchemy中,可以通过UniqueConstraint来定义联合唯一键。以下是一个简单的代码示例,展示了如何在一个学生选课表中定义联合唯一键。 fromsqlalchemyimportcreate_engine,Column,Integer,String,ForeignKey,UniqueConstraintfromsqlalchemy.ext.declarativeimportdeclarative_basefromsqlalchemy.ormimportsessionmaker ...
( logical_expression ) ] <column_set_definition> ::= column_set_name XML COLUMN_SET FOR ALL_SPARSE_COLUMNS ::= [ CONSTRAINT constraint_name ] { { PRIMARY KEY | UNIQUE } [ CLUSTERED | NONCLUSTERED ] ( column_name [ ASC | DESC ] [ ,... n ] ) [ WITH FILLFACTOR = fillfactor...
( seed , increment ) ] ] [ ROWGUIDCOL ] [ column_constraint ] [ ...n ] <column_constraint> ::= { [ NULL | NOT NULL ] | [ PRIMARY KEY | UNIQUE ] | CHECK ( logical_expression ) } ::= { { PRIMARY KEY | UNIQUE } ( column_name [ , ...n ] ) | CHECK ( logical_expre...