How to Create a View on a TEMP Table in SQL?

In SQL Server, TEMP tables are used to store data temporarily during the session in which they are created. These tables are especially useful for storing intermediate results or simplifying complex queries. In this article, We will learn about whether can we create a view on a TEMP table in SQL Server in detail and so on.

What is a TEMP Table in SQL Server?

A TEMP table in SQL Server is a special kind of table that is created for temporary storage of data. TEMP tables can either be local (denoted by #) or global (denoted by ##).

• Local TEMP tables (e.g., #TempTable) are visible only to the session that created them.
• Global TEMP tables (e.g., ##TempTable) are visible to all sessions but they are dropped when the session that created them is closed.

Example of Creating a TEMP Table

CREATE TABLE #TempTable (    ID INT,    Name VARCHAR(50));
INSERT INTO #TempTable (ID, Name)
VALUES (1, 'Alice'), (2, 'Bob');

What is a View in SQL Server?

A view in SQL Server is a virtual table that represents the result of a query. Unlike regular tables views do not store data physically but present data from one or more tables in a way that simplifies complex queries. Views can be created using the CREATE VIEW statement.

Example of Creating a View

CREATE VIEW EmployeeView ASSELECT ID, Name
FROM EmployeeTable
WHERE Age > 30;

Explanation: This above query creates a view named `EmployeeView` that retrieves the `ID` and `Name` of employees from `EmployeeTable` whose age is greater than 30 and allows easier reuse of this filtered data in future queries.

Can We Create a View on a Temporary Table?

The answer is No, we cannot create a view directly on a temporary table in SQL Server because of below reasons:

• Scope Limitations: Temporary tables are session-specific which means they only exist during the session in which they are created. Views on the other hand are intended to persist across sessions and are part of the schema. Therefore, a view cannot reference a session-bound temporary table since views need to be accessible to all users and persist beyond the session.
  
• SQL Server Error: If we try to create a view based on a temporary table, we will receive an error like the following:

Msg 208, Level 16, State 1, Line 1
Invalid object name '#TempTable'.

This error occurs because SQL Server cannot find the temporary table when creating a view since temporary tables are not available outside the session where they were created.

Example of Create a View on a Temporary Table

-- Create a temporary table
CREATE TABLE #TempEmployee (
    ID INT,
    Name VARCHAR(50)
);

-- Attempt to create a view based on the temporary table (this will fail)
CREATE VIEW TempEmployeeView AS
SELECT * 
FROM #TempEmployee;

Error Message:

Msg 208, Level 16, State 1, Line 5
Invalid object name '#TempEmployee'.

This error occurs because a view cannot reference the #TempEmployee table since it's a temporary table that only exists within the session where it was created.

Why Doesn't SQL Server Allow Views on Temporary Tables?

• Persistence: Temporary tables are created and dropped automatically during the session. Views, however, need to be persistent objects within the database schema. Allowing a view to depend on a temporary table would break this persistence model because views are expected to be available across sessions, unlike temporary tables.
  
• Session Specific: Temporary tables only exist for the duration of a session, while views are meant to be reusable by all users and can be referenced at any time. Since views require the data to be accessible beyond the session, SQL Server does not allow creating a view on a temporary table.

Conclusion

In SQL Server, we cannot create a view on a temporary table due to the session-specific nature of temporary tables and the persistent nature of views. However, if you need a similar effect, you can either use a permanent table, table variables or global temporary tables based on our specific requirements.

Always carefully evaluate whether the need for a view-based approach justifies using permanent tables or other alternatives to achieve the desired functionality.