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- Owner of the constraint definition. 约束定义的所有者。
- The following excerpt of a CREATE TABLE statement shows the definition of the Name column, specifying a UNIQUE constraint on this column to make sure the values are unique. 一个CREATE TABLE语句的以下节选显示Name列的定义,对该列指定了UNIQUE约束,以确保值是唯一的。
- This class can be used to identify a unique constraint among a set of elements. 此类可用于标识一组元素中的唯一约束。
- The Unique Constraint or Foreign Key Constraint dialog box is displayed. 即显示“唯一约束”或“外键约束”对话框。
- A computed column cannot be used as a DEFAULT or FOREIGN KEY constraint definition or with a NOT NULL constraint definition. 计算列不能用作DEFAULT或FOREIGN KEY约束定义,也不能与NOT NULL约束定义一起使用。
- The ALTER INDEX statement can be used to rebuild an index part of a constraint definition; the constraint does not have to be dropped and added again with ALTER TABLE. ALTER INDEX语句可用于重新生成约束定义的索引部分;而不必再使用ALTER TABLE来删除和添加约束。
- Index imposing the UNIQUE constraint on the column designated as the unique key column. 对于指定为唯一键列的列施加UNIQUE约束的索引。
- Add or drop PRIMARY KEY or UNIQUE constraints. 添加或删除PRIMARY KEY或UNIQUE约束。
- Unique constraints are also called keys. 唯一约束也称为键。
- However, changing the length of a variable-length column used in a CHECK or UNIQUE constraint is allowed. 但是,允许更改用于CHECK或UNIQUE约束中的长度可变的列的长度。
- This set of columns may be generated from a base table primary key, a unique constraint or a unique index. 这组列可以从基表主键、唯一约束或唯一索引生成。
- All of the tables in the main data connection must contain a primary key, unique constraint, or unique index. 主数据连接中的所有表都必须包含一个主键、唯一约束或唯一索引。
- Columns of a unique index are allowed to be NULL, while columns in a unique constraint are not. 唯一索引的列可以为NULL,而唯一约束的列不能为NULL。
- In order to create a foreign key relationship, at least one of the two tables must have a primary key or unique constraint defined. 要创建外键关系,两个表中必须至少有一个定义了主键或唯一约束。
- A unique index, UNIQUE constraint, or PRIMARY KEY constraint cannot be created if duplicate key values exist in the data. 如果数据中存在重复的键值,则不能创建唯一索引、UNIQUE约束或PRIMARY KEY约束。
- An index created as part of a PRIMARY KEY or UNIQUE constraint is automatically given the same name as the constraint name. 创建为PRIMARY KEY或UNIQUE约束的一部分的索引将自动给定与约束名称相同的名称。
- Create a unique constraint to ensure no duplicate values are entered in specific columns that do not participate in a primary key. 创建唯一约束可确保在不参与主键的特定列中不输入重复值。
- When you attach a unique constraint to a column allowing null values, you ensure that at most one row will have a null value in the constrained column. 当将唯一约束附加到允许空值的列时,请确保在约束的列中最多有一行包含空值。
- Because the Regular Expression generator is not guaranteed to produce unique values, you cannot use it to fill a user-defined type column that has a unique constraint. 由于正则表达式生成器无法保证生成唯一值,因此您不能使用它来填充具有唯一约束的用户定义的类型列。
- If a table already exists, you can add a UNIQUE constraint, provided that the column or combination of columns that make up the UNIQUE constraint contains only unique values. 如果表已经存在,可以添加UNIQUE约束(假设组成UNIQUE约束的列或列组合仅包含唯一的值)。