SQL Server automatically creates indexes when PRIMARY KEY and UNIQUE constraints are defined on table columns. For example, when you create a table with a UNIQUE constraint, Database Engine automatically creates
SQL Server automatically creates indexes when PRIMARY KEY and UNIQUE constraints are defined on table columns. For example, when you create a table with a UNIQUE constraint, Database Engine automatically creates a nonclustered index. If you configure a PRIMARY KEY, Database Engine automatically creat...
实际上,您可以把索引理解为一种特殊的目录。微软的SQL SERVER提供了两种索引:聚集索引(clustered index,也称聚类索引、簇集索引)和非聚集索引(nonclustered index,也称非聚类索引、非簇集索引)。下面,我们举例来说明一下聚集索引和非聚集索引的区别: 其实,我们的汉语字典的正文本身就是一个聚集索引。比如,我们要查"...
Clustered : 資料與索引是儲放在一起,每個表格中只能有一個,資料必會排序過,速度快。 NonClustered:資料與索引為分開儲放,就像C++的指標,索引會存儲資料的位置,資料可能沒有排序。 叢集索引結構 在SQL Server 中,索引的結構為 B 型樹狀目錄。索引 B 型樹狀目錄中的每個分頁稱為索引節點。B 型樹狀目錄的頂部節點...
When you create a UNIQUE constraint, a unique nonclustered index is created to enforce a UNIQUE constraint by default. You can specify a unique clustered index if a clustered index on the table doesn't already exist. An index created as part of the constraint is automatically given the same...
1. 什么是聚合索引(clustered index) / 什么是非聚合索引(nonclustered index)? 2. 聚合索引和非聚合索引有什么区别? 深入浅出理解索引结构 实际上,您可以把索引理解为一种特殊的目录。微软的SQL SERVER提供了两种索引:聚集索引(clustered index,也称聚类索引、簇集索引)和非聚集索引(nonclustered index,也称非聚类...
CREATE NONCLUSTERED INDEX IX_EMP_NAME ON EMPLOYEES(NAME) -- 再次执行WHERE查询并含实际执行计划。 SELECT * FROM EMPLOYEES WHERE NAME = 'ABC 874000' 1. 2. 3. 4. 5. 6. Key映射查找 查询例子同上。 上例的执行计划中我们可以看到key lookup过程,这个映射查找出现的原因是我们的查询里name字段虽然可以...
When you create aUNIQUEconstraint, a unique nonclustered index is created to enforce aUNIQUEconstraint by default. You can specify a unique clustered index if a clustered index on the table doesn't already exist. An index created as part of the constraint is automatically given the same name ...
Using SQL Server Management Studio To create a nonclustered index by using the Table Designer In Object Explorer, expand the database that contains the table on which you want to create a nonclustered index. Expand theTablesfolder. Right-click the table on which you want to create a nonclust...
Using SQL Server Management Studio To create a nonclustered index by using the Table Designer In Object Explorer, expand the database that contains the table on which you want to create a nonclustered index. Expand theTablesfolder. Right-click the table on which you want to create a nonclust...