Can You Create Indexes on SQL Server 2000 Table Variables?

Detailed explanation of SQL Server 2000 table variable index

Introduction

In SQL Server development, whether table variables can create indexes has always been a common question. This article delves into the details of table variable indexes, focusing on SQL Server 2000.

Can indexes be created on table variables?

For SQL Server 2000, the answer is yes. Indexes can be created on table variables using implicit methods, primarily through the use of unique key or primary key constraints.

Constraint-based indexing

Both unique key and primary key constraints implicitly create unique indexes. The difference is the allowability of null values ​​for participating columns. The primary key must be defined on a non-null value column, and the unique constraint allows null value columns.

Specify index attribute

While the physical implementation of an index created by a constraint is determined by a default value, it can be overridden by explicitly specifying the CLUSTERED or NONCLUSTERED option in the constraint declaration. This allows some control over the type of index created.

Different types of indexes

In SQL Server 2000 - 2012, the following types of indexes can be created implicitly on table variables:

• Unique clustered index
• Unique non-clustered index on the heap
• Unique non-clustered index on clustered index

You cannot use constraints to directly create non-unique clustered and non-clustered indexes on table variables.

Solution to non-unique non-clustered index

To simulate a non-unique non-clustered index, create a unique index on a combination of the relevant column and the clustered index key (the clustered index key is automatically added on a non-unique index anyway).

Add unique identifier manually

For non-unique clustered indexes, you can manually add an IDENTITY column as a unique identifier. However, this is not exactly equivalent to a non-unique clustered index, as it affects all rows, not just the rows that require uniqueness.

Conclusion

In SQL Server 2000, you can create indexes on table variables using a constraint-based approach. Understanding the different types of indexes and how they are implicitly implemented can help optimize queries involving table variables.

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