alter table 表名称 add constraint 约束名称 增加的约束类型 (列名) 例子: alter table emp add constraint xxx check(age>20) 3.unique约束: 这样的约束就是给列的数据追加的不重复的约束类型 格式: alter table 表名 add constraint 约束名称 约束类型(列名) 比方说可以给ename列加个unique,让ename列的数据...
UNIQUE [CLUSTERED | NONCLUSTERED] (column_name1[, column_name2,…,column_name16]) 例7-5:定义一个员工信息表,其中员工的身份证号具有惟一性。 create table employees ( emp_id char(8), emp_name char(10) , emp_cardid char(18), constraint pk_emp_id primary key (emp_id), constraint uk_...
Add a Unique ConstraintWrite a SQL query to add a unique constraint to a column in an existing table.Solution:-- Add a unique constraint to the "Name" column to ensure no duplicate names. ALTER TABLE Employees -- Specify the table to modify. ADD CONSTRAINT UC_Name UNIQUE (Name)...
The ordered-list of column names for the columns that make up the constraint. C# Copy public virtual string[] Columns { get; set; } Property Value String[] Applies to उत्पादसंस्करण Entity Framework Core 1.0, 1.1, 2.0, 2.1, 2.2, 3.0...
SQL Server有两种类型的文件组:· 主文件组:包含主数据文件和任何没有明确分配给其他文件组的其他文件。系统表的所有页均分配在主文件组中。·用户定义文件组:用户定义文件组是通过在CREATE DATABASE或ALTER DATABASE语句中使用FILEGROUP关键字指定的任何文件组。
2. SQL ADD COLUMN示例 以下语句创建一个名为candidate的新表: CREATETABLEcandidates ( idINTPRIMARYKEY, first_nameVARCHAR(100)NOTNULL, last_nameVARCHAR(100)NOTNULL, emailVARCHAR(255)NOTNULLUNIQUE); 要将phone列添加到candidates表,请使用以下语句: ...
83 Check constraint only one of three columns is non-null 0 unique key violation occuring on a unique value combination 5 Unable to drop non-PK index because it is referenced in a foreign key constraint 19 NVARCHAR column as PRIMARY KEY or as UNIQUE column 1 Should...
« SQL Server Bigint Max Value Conditional Where Clause » To add a constraint to an existing table use the alter table statement with the add constraint command. There are four different types of constraints:Primary Key Constraints – Enforces unique values for specified column, can be ...
CONSTRAINT name Optionally specifies a name for the constraint. The name must be unique within the schema. If no name is provided Azure Databricks will generate one. PRIMARY KEY ( key_column [ TIMESERIES ] [, ...] ) [ constraint_option [...] ] Applies to: Unity Catalog onl...
privatevoidAddConstraint(DataTable table){ UniqueConstraint uniqueConstraint;// Assuming a column named "UniqueColumn" exists, and// its Unique property is true.uniqueConstraint =newUniqueConstraint( table.Columns["UniqueColumn"]); table.Constraints.Add(uniqueConstraint); } ...