You cannot create a unique index on a single column if that column contains NULL in more than one row. Similarly, you cannot create a unique index on multiple columns if the combination of columns contains NULL in more than one row. These are treated as duplicate values for indexing purposes...
Consider the order of the columns if the index contains multiple columns. The column that is used in the WHERE clause in an equal to (=), greater than (>), less than (<), or BETWEEN search condition, or participates in a join, should be placed first. Additional columns should b...
如果对表定义了聚集索引,则非聚集索引始终包含聚集索引列。 有关详细信息,请参阅 Create Indexes with Included Columns。允许除 text、 ntext和image之外的所有数据类型。 从 SQL Server 2012 (11.x) 和 Azure SQL 数据库开始,如果任何一个指定的非键列是 varchar(max)、nvarchar(max) 或 varbinary(max) 数据...
有关详细信息,请参阅 CREATE COLUMNSTORE INDEX。 有关有序列存储索引可用性,请参阅 列存储索引:概述。 从SQL Server 2016 (13.x) 开始,可以将表创建为聚集列存储索引。 再也不需要先创建行存储表,然后将其转换为聚集列存储索引。 有关列存储索引设计指南的信息,请参阅列存储索引 - 设计指南。
An index is an on-disk structure associated with a table or view that speeds retrieval of rows from the table or view. An index contains keys built from one or more columns in the table or view. These keys are stored in a structure (B-tree) that enables SQL Server to find the row ...
SQL Server解惑——标识列的限制和跳号现象 1:每个表只能创建一个标识列。 如下测试所示,如果表中有一个标识列,新增一个标识列就会遇到错误“Multiple identity columns specified for table 'TEST'. Only one identity column per table is allowed.“
You cannot create a unique index on a single column if that column contains NULL in more than one row. Similarly, you cannot create a unique index on multiple columns if the combination of columns contains NULL in more than one row. These are treated as duplicate values for indexing purposes...
Syntax for SQL Server and Azure SQL Database:syntaxsql Copy -- Create a clustered columnstore index on disk-based table. CREATE CLUSTERED COLUMNSTORE INDEX index_name ON { database_name.schema_name.table_name | schema_name.table_name | table_name } [ ORDER (column [ , ...n ] ) ] ...
Syntax for SQL Server and Azure SQL Database:syntaxsql Copy -- Create a clustered columnstore index on disk-based table. CREATE CLUSTERED COLUMNSTORE INDEX index_name ON { database_name.schema_name.table_name | schema_name.table_name | table_name } [ ORDER (column [ , ...n ] ) ] ...
The CREATE INDEX statement creates a partitioning index or a secondary index and an index space at the current server. The columns included in the key of the index are columns of a table at the current server. Invocation for CREATE INDEX This statement can be embedded in an application ...