ALTER table tableName ADD INDEX indexName(columnName) 1. 在创建表的时候就指定索引 CREATE TABLE mytable( ID INT NOT NULL, username VARCHAR(16) NOT NULL, INDEX [indexName] (username(length)) ); 1. 2. 3. 4. 5. 删除索引: DROP INDEX [indexName] ON mytable; 1. 唯一索引 区别: 索引...
不用担心,Sql Server 还提供了其他一些途径来控制系统如何产生查询计划. 这其中,包括 Query hint, 和 Join hint. 如果这些还不够,你还可以更进一步使用Plan Guide. 关于这些,不在此多讲. 以下是本性能试验中使用的一些代码,是我在Tsuranoff先生的代码的基础上改进的结果. ---create table and populate dataCR...
The trickiest problems, though, come with increasing size of the tables, because, before SQL Server 2016, you couldn’t declare an index explicitly, and the indexes that enforced the UNIQUE and PRIMARY KEY constraints didn’t have distribution indexes maintained on them. Now you can create cert...
Temporary Tables And Table Variables In SQL 基本常识 1. 局部临时表(#开头)只对当前连接有效,当前连接断开时自动删除 2. 全局临时表(##开头)对其它连接也有效,在当前连接和其他访问过它的连接都断开时自动删除 3. 临时表就像普通表一样,它可以做索引等等 4. 临时表存在 tempdb database, 表变量存在 memory...
Create a nonclustered index with a unique constraint and specify the sort order SQL Copy CREATE UNIQUE INDEX index1 ON schema1.table1 (column1 DESC, column2 ASC, column3 DESC); Key scenario: Starting with SQL Server 2016 (13.x), in Azure SQL Database, and in Azure SQL Managed Inst...
Temporary tables Show 12 more Applies to: SQL Server Azure SQL Database Azure SQL Managed Instance SQL database in Microsoft Fabric Creates a new table in the database. Note For reference to Warehouse in Microsoft Fabric, visit CREATE TABLE (Fabric Data Warehouse). For reference to Azure Syn...
記憶體優化 CREATE TABLE 語法: syntaxsql 複製 CREATE TABLE { database_name.schema_name.table_name | schema_name.table_name | table_name } ( { <column_definition> | [ <table_constraint> ] [ ,... n ] | [ <table_index> ] [ ,... n ] } [ PERIOD FOR SYSTEM_TIME ( system_star...
When you create temporary tables, you won’t see them in the current database you’re working on. SQL Server puts them into TempDB. Let’s try it using the previous example: USE AdventureWorks; GO SELECT a.ProductID ,a.Name as ProductName ...
索引(Index) I/0开销 作用域(scope) 存儲位置 其他 例子描述 约束(Constraint) 在临时表和表变量,都可以创建Constraint。针对表变量,只有定义时能加Constraint。 e.g.在Microsoft SQL Server Management Studio(MSSMS)查询中,创建临时表并建Constraint场景,<脚本S1.> ...
CTEs / Common Table Expressions CTE指的是我们,通过With()的形式,在一个query的运行区间,创建一个暂时的表。并且使用CTE也能够完美的代码可阅读性和简洁性。 We creates a temporary table for duration of the query 例子如下,我们创建了一个叫Student的CTE,它能够在紧接着它的下一个query中使用: WITH Studen...