Index vs. constraintFirst, let's verify to ourselves that a unique index and a unique constraint really do have the same effect on a table by adding both of them to a sample table and inspecting the results. Let
Index vs. constraint First, let's verify to ourselves that a unique index and a unique constraint really do have the same effect on a table by adding both of them to a sample table and inspecting the results. Let's choose the publishers table in the pubs database and create the index ...
UniqueConstraint.cs 使用指定的UniqueConstraint初始化DataColumn类的新实例。 C# publicUniqueConstraint(System.Data.DataColumn column); 参数 column DataColumn 要约束的DataColumn。 示例 以下示例创建一个新的UniqueConstraint,并将其ParentKeyConstraint分配给 的DataRelation属性。
A unique constraint ensures no duplicate values are entered into specified columns that are not a table's primary key. For example, in the employee table in which the emp_id column is the primary key, you can define a unique constraint that requires entries in the Social Security number (...
UniqueConstraint.IndexOptions 屬性 發行項 2011/08/12 本文內容 語法 備註 .NET Framework 安全性 請參閱 取得索引選項的清單。 命名空間:Microsoft.Data.Schema.ScriptDom.Sql 組件:Microsoft.Data.Schema.ScriptDom.Sql (在 Microsoft.Data.Schema.ScriptDom.Sql.dll 中) ...
ConstraintIdentifier取得或設定條件約束的名稱。 (繼承自Constraint)。 FileStreamOn取得或設定檔案資料流的選擇性規格。 FirstTokenIndex取得或設定第一個語彙基元索引。 (繼承自TSqlFragment)。 FragmentLength取得片段長度。 (繼承自TSqlFragment)。 IndexOptions取得索引選項的清單。
UniqueConstraint Class Reference Feedback Definition Namespace: System.Data Assemblies: netstandard.dll, System.Data.Common.dll Source: UniqueConstraint.cs Represents a restriction on a set of columns in which all values must be unique. C# Copy public class UniqueConstraint : System.Data....
UniqueConstraint 型別會公開下列成員。方法展開資料表 名稱說明 Accept 指定之訪客的進入點。 (覆寫 TSqlFragment.Accept(TSqlFragmentVisitor)。) AcceptChildren 在具有指定之訪客的子系上呼叫 Accept。 (覆寫 Constraint.AcceptChildren(TSqlFragmentVisitor)。) Equals 判斷指定的 Object 和目前的 Object 是否...
ERROR: duplicate key value violates unique constraint "i_nulltest2" DETAIL: Key (x, (y IS NULL))=(2, t) already exists.INSERT INTO nulltest2 VALUES (2, 3); INSERT INTO nulltest2 VALUES (2, 3); Thei_nulltest2index allows only oneynull value for eachxvalue. This can actually b...
using CREATE UNIQUE INDEX. Creating unique indexes through a primary key or unique constraint is not guaranteed to create a new index, and the index they create is not guaranteed to be a unique index.It is just that in a unique index, the rowid is not considered "part of the key" and...