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 ...
Use SQL Server Management StudioIn Object Explorer, right-click the table to which you want to add a unique constraint, and select Design. In Table Designer, select the row selector for the database column you want to define as the primary key. If you want to select multiple columns, ...
alter table orders add constraint fk_employee_creator_order foreign key (eid) references employee(employeeid) 使用表自引用 表内至少要有一行数据才可以这么做 alter table employee add constraint fk_employee_has_manager foreign key (managerid) references employee(employeeid) 创建表的时候做表自引用 就可...
You can create a check constraint in a table to specify the data values that are acceptable in one or more columns in SQL Server by using SQL Server Management Studio or Transact-SQL. For more information on adding column constraints, see ALTER TABLE column_constraint. For more information, ...
Use SQL Server Management Studio InObject Explorer, expand the table to which you want to add a check constraint, right-clickConstraintsand selectNew Constraint. In theCheck Constraintsdialog box, select in theExpressionfield and then select the ellipses(...). ...
指定表达式的排序规则。 此排序规则必须是 SQL Server 支持的 Windows 排序规则之一。 有关 SQL Server 支持的 Windows 排序规则列表,请参阅Windows 排序规则名称(Transact-SQL)。 NULL|NOT NULL 指定列中是否允许使用NULL值。 默认为NULL。 [CONSTRAINTconstraint_name]DEFAULTconstant_expression ...
2)SQL约束(6 个) (1)NOT NULL(一种写法) createtablecourse( cidintnotnull,cnamevarchar(255), tidint); (2)UNIQUE(三种写法) createtablecourse( cidintnotnull, cnamevarchar(255)notnullunique,tidint,unique(cid),CONSTRAINTuc_courseIDunique(cid, tid)--命名多列约束); ...
不過,在啟用 clr 啟用選項之前,您無法在 SQL Server 中執行這些參考。 若要啟用這個選項,請使用 sp_configure。 自主資料庫中無法使用此選項。<> table_type_definition ( { <column_definition column_constraint><| <> computed_column_definition } [ table_constraint> ] [ <, ...n ]...
To maintain compatibility with earlier versions of SQL Server, a constraint name can be assigned to a DEFAULT. constant_expression A constant, NULL, or a system function that is used as the default value for the column. memory_optimized_constant_expression A constant, NULL, or a system ...
定义不联接的约束的列称为分区列。 分区列可以在基础表中具有不同的名称。 约束必须处于启用和信任状态,以使它们满足分区依据列的上述条件。 如果禁用了约束,请使用选项ALTER TABLE重新启用约束检查CHECK CONSTRAINT *constraint_name*,并使用WITH CHECK该选项来验证它们。 以下示例...