Understanding SQL Server Temp Table for Dev

Dear Dev, in this article, we will explore the concept of SQL Server temp table. As a developer, you must have come across scenarios where you need to store data temporarily, and SQL Server temp table is a perfect solution for that. We will cover everything you need to know about temp tables, including the benefits, how to create and use them efficiently, and best practices to follow.

What is a SQL Server Temp Table?

A SQL Server temp table is a temporary table that is created and used within a single session or connection. It is a schema-bound object that allows you to store and manipulate data temporarily in a SQL Server database. Temp tables are stored in the tempdb database, which is a system database designed to hold the temporary objects created by SQL Server.

There are two types of temp tables in SQL Server:

Local Temp Table	Global Temp Table
A local temp table is available only in the current session.	A global temp table is available to all sessions.
The name of a local temp table starts with #.	The name of a global temp table starts with ##.

Benefits of Using SQL Server Temp Tables

SQL Server temp tables offer several benefits:

• They allow you to store data temporarily, which can be useful in various scenarios, such as storing intermediate results or running complex queries.
• Temp tables can improve query performance by reducing the number of table scans and joins, and by caching intermediate results.
• They are easy to create and use, and do not require any special permissions or settings.
• Temp tables can be used in stored procedures, functions, and dynamic SQL statements.

Creating a SQL Server Temp Table

Creating a SQL Server temp table is similar to creating a regular table. Here is the basic syntax:

CREATE TABLE #TempTable (Column1 datatype,Column2 datatype,...)

You can also create a global temp table by using the ## prefix:

CREATE TABLE ##TempTable (Column1 datatype,Column2 datatype,...)

Column Data Types

The column data types in a temp table can be any valid data type in SQL Server, including user-defined data types, but they must be explicitly defined. Here are some common data types:

Data Type	Description
INT	Integer
VARCHAR(n)	Variable-length character string with a maximum length of n
DECIMAL(p, s)	Fixed-point decimal with p total digits and s decimal places
DATE	Date value without a time component

Using SQL Server Temp Tables

Once you have created a temp table, you can use it just like a regular table. You can insert, update, delete, and select data from the temp table using SQL statements. Here are some examples:

Inserting Data

You can insert data into a temp table using the INSERT statement:

INSERT INTO #TempTable (Column1, Column2, ...)VALUES (Value1, Value2, ...)

You can also insert data from a query:

INSERT INTO #TempTable (Column1, Column2, ...)SELECT Column1, Column2, ...FROM SourceTable

Updating Data

You can update data in a temp table using the UPDATE statement:

UPDATE #TempTableSET Column1 = Value1, Column2 = Value2, ...WHERE Condition

Deleting Data

You can delete data from a temp table using the DELETE statement:

DELETE FROM #TempTableWHERE Condition

Querying Data

You can select data from a temp table using the SELECT statement:

SELECT Column1, Column2, ...FROM #TempTableWHERE Condition

Best Practices for Using SQL Server Temp Tables

Here are some best practices to follow when using SQL Server temp tables:

• Use temp tables only when necessary. Avoid using them for small or simple queries.
• Limit the size of temp tables to reduce the impact on tempdb.
• Drop temp tables when they are no longer needed to free up resources.
• Avoid using SELECT INTO to create temp tables, as it can cause performance issues and table locking.
• Use appropriate indexing on temp tables to improve query performance.
• Avoid using temp tables in high-concurrency environments or on heavily loaded servers.

FAQ

What is the scope of a temp table?

The scope of a temp table is limited to the current session or connection. Local temp tables are visible only to the current session, while global temp tables are visible to all sessions.

How long do temp tables last?

Temp tables are automatically dropped when the connection that created them is closed or when the session ends. You can also drop them explicitly using the DROP TABLE statement.

Can I use temp tables in a transaction?

Yes, you can use temp tables in a transaction. Temp tables behave like regular tables in transactions, and changes made to them are rolled back or committed along with other transactional changes.

What is the difference between a temp table and a table variable?

A table variable is also a temporary object that is used to store data temporarily, but it is not stored in tempdb. Instead, it is created in memory and is only visible within the current batch, stored procedure, or function. Table variables are useful for small amounts of data, but they can cause performance issues with large datasets.

Can I use temp tables in a view?

No, you cannot use temp tables in a view. Views are not allowed to create, modify, or drop temp tables.

Conclusion

SQL Server temp tables are a powerful and flexible tool for storing and manipulating data temporarily. They offer several benefits, including improved performance and flexibility, and are easy to create and use. By following best practices and using them judiciously, you can take advantage of temp tables to streamline your SQL code and make it more efficient and effective.