A unique clustered index must be created on a view before any other indexes can be defined on the same view. Creating a unique clustered index on a view physically materializes the view. A table or view is allowed one clustered index at a time.Ī view with a unique clustered index is called an indexed view. The bottom, or leaf, level of the clustered index contains the actual data rows of the table. CLUSTEREDĬreates an index in which the logical order of the key values determines the physical order of the corresponding rows in a table. Columns that are used in a unique index should be set to NOT NULL, because multiple null values are considered duplicates when a unique index is created. Duplicate values must be removed before a unique index can be created on the column or columns. If this is tried, the Database Engine displays an error message. The Database Engine doesn't allow creating a unique index on columns that already include duplicate values, whether or not IGNORE_DUP_KEY is set to ON. A clustered index on a view must be unique. A unique index is one in which no two rows are permitted to have the same index key value. Arguments UNIQUEĬreates a unique index on a table or view. To view Transact-SQL syntax for SQL Server 2014 (12.x) and earlier versions, see Previous versions documentation. Syntax for Azure Synapse Analytics and Parallel Data WarehouseĬREATE CLUSTERED COLUMNSTORE INDEX index_name Use the syntax structure specified in instead. The backward compatible relational index syntax structure will be removed in a future version of SQL Server.Īvoid using this syntax structure in new development work, and plan to modify applications that currently use the feature. Transact-SQL syntax conventions Syntax Syntax for SQL Server, Azure SQL Database, Azure SQL Managed Instance CREATE INDEX index_name For more information, see Columnstore Indexes - Data Warehouse. Starting with SQL Server 2016 (13.x) and SQL Database, you can use a nonclustered index on a columnstore index to improve data warehousing query performance. Any examples referencing unique constraints are only applicable to SQL Server and SQL Database.įor information on index design guidelines, refer to the SQL Server Index Design Guide.Ĭreate a nonclustered index on a table or view CREATE INDEX index1 ON schema1.table1 (column1) Ĭreate a clustered index on a table and use a 3-part name for the table CREATE CLUSTERED INDEX index1 ON 1 (column1) Ĭreate a nonclustered index with a unique constraint and specify the sort order CREATE UNIQUE INDEX index1 ON schema1.table1 (column1 DESC, column2 ASC, column3 DESC) For more information, see the SQL Server and Azure SQL index architecture and design guide.Īzure Synapse Analytics and Analytics Platform System (PDW) currently don't support unique constraints. This does not apply to columnstore indexes or in-memory data stores. In rowstore indexes, SQL Server implements a B+ tree. SQL Server documentation uses the term B-tree generally in reference to indexes.
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