主键索引(必须指定为“PRIMARY KEY”,没有PRIMARY Index)、 唯一索引(unique index,一般写成unique key)、 普通索引(index,只有这一种才是纯粹的index)等,也是基于是不是把index看作了key。 比如create table t(id int,unique indexinx_tx_id (id));--index当作了key使用 (2)最重要的也就是,不管如何描述,...
SQL Server 2016 (13.x) and later Azure SQL Database Azure SQL Managed Instance You can define a primary key in the SQL Server Database Engine by using SQL Server Management Studio or Transact-SQL. Creating a primary key automatically creates a corresponding unique clustered index. However, you...
ALTER TABLE myIndex ADD INDEX name_city_age (vc_Name(10),vc_City,i_Age);--注意了,建表时,vc_Name长度为50,这里为什么用10呢?因为一般情况下名字的长度不会超过10,这样会加速索引查询速度,还会减少索引文件的大小,提高INSERT的更新速度。 执行T-SQL时,MySQL无须扫描任何记录就到找到唯一的记录!! 肯定...
PRIMARY,INDEX,UNIQUE,FULLTEXT,SPAI。。。⼀、介绍⼀下索引的类型 Mysql常见索引有：主键索引、唯⼀索引、普通索引、全⽂索引、组合索引 PRIMARY KEY（主键索引） ALTER TABLE `table_name` ADD PRIMARY KEY ( `column` ) UNIQUE(唯⼀索引) ALTER TABLE `table_name` ADD UNIQUE (`column`)INDEX(普通...
In a table object, any keys defined after the primary key are called secondary keys. All keys defined in a table extension object are considered secondary keys. A secondary key is implemented on SQL Server using a structure that is called an index. This structure is like an index that is ...
more if desired, with options likeminvalueandmaxvalueto of course indicate extreme values, and evenCYCLE, which allows the sequence to “loop around” once it reaches themaxvalue, returning back to thestartvalue and beginning the climb all over again. Far more information can be found in the...
SQL CREATETABLE[Production].[TransactionHistoryArchive1] ( TransactionIDINTIDENTITY(1,1)NOTNULL,CONSTRAINTPK_TransactionHistoryArchive1_TransactionID PRIMARYKEYCLUSTERED (TransactionID) ); Create a nonclustered primary key with separate clustered index in a new table ...
The primary XML index indexes all tags, values, and paths within the XML instances in an XML column. To create a primary XML index, the table in which the XML column occurs must have a clustered index on the primary key of the table. SQL Server uses this primary key to correlate rows...
Primary keys are required in Microsoft SQL Server Analysis Services to uniquely identify records in a table, identify key columns in dimension tables and to support relationships between tables, views and named queries. These relationships are used to construct queries for retrieving data and metadata...
When you specify a PRIMARY KEY constraint for a table, the Database Engine enforces data uniqueness by creating a unique index for the primary key columns. This index also permits fast access to data when the primary key is used in queries. Therefore, the primary keys that are chosen must...