Hello readers! Welcome to our comprehensive guide on temp tables in SQL Server. This article aims to provide you with a complete understanding of temp tables, their usage, benefits, and drawbacks. By the end of this guide, you will have a solid understanding of how temp tables can help you with your SQL tasks. Let’s dive in!
What Are Temp Tables?
Before we dive deep into the world of temp tables, let us first understand what they are. Temp tables, also known as temporary tables, are a type of table that is created in the tempdb database in SQL Server. They are used to store and manipulate temporary data within a session or a batch. Temp tables are created and destroyed automatically when the session or batch ends.
Unlike regular tables that store data permanently, temp tables hold data temporarily, making them ideal for use in complex queries and procedures that require temporary storage of data.
Types of Temp Tables
In SQL Server, there are two types of temp tables that you can create:
| Temp Table Type | Description |
|---|---|
| Local Temp Tables | These tables are created with a single “#” symbol as a prefix to the table name and are only visible within the current session. They are automatically deleted when the session ends. |
| Global Temp Tables | These tables are created with a “##” prefix to the table name and are visible to all sessions on a given SQL Server. They are deleted when the last session referencing them ends. |
How to Create Temp Tables
Creating temp tables in SQL Server is a straightforward process. Let’s look at an example:
CREATE TABLE #TempTable
(
ID INT,
Name VARCHAR(50)
)The above code creates a local temp table called #TempTable with two columns, ID and Name. It’s that simple!
Inserting Data into Temp Tables
After creating a temp table, the next step is to insert data into it. The process is similar to inserting data into a regular table. Let’s look at an example:
INSERT INTO #TempTable
VALUES (1, 'John'), (2, 'Jane'), (3, 'Bob')The above code inserts three rows into the #TempTable table. You can also use the SELECT INTO statement to insert data into a temp table:
SELECT *
INTO #TempTable
FROM Customers
WHERE Country = 'USA'The above code selects all customers from the Customers table who are from the USA and inserts them into the #TempTable table.
Querying Temp Tables
Once you have inserted data into a temp table, you can query it just like a regular table. Let’s look at an example:
SELECT *
FROM #TempTable
WHERE Name = 'John'The above code selects all rows from the #TempTable table where the Name column equals ‘John’.
Benefits of Using Temp Tables
Temp tables offer several benefits that make them a valuable tool in SQL Server:
| Benefits of Temp Tables |
|---|
| Temporary storage of data |
| Improved performance in complex queries and procedures |
| Isolation of data within sessions and batches |
| Reduced table locking and blocking |
FAQs
Q: How long do temp tables last?
A: Temp tables last for the duration of the session or batch in which they were created. Once the session or batch ends, the temp table is automatically deleted.
Q: Can temp tables be indexed?
A: Yes, you can create indexes on temp tables just like regular tables. However, keep in mind that indexes on temp tables are only useful if the data in the table is large enough to require indexing.
Q: Can multiple sessions access the same temp table?
A: If you create a global temp table, then all sessions on the SQL Server can access the table. However, if you create a local temp table, then only the session that created the table can access it.
Q: Is it possible to rename a temp table?
A: Yes, you can use the sp_rename system stored procedure to rename a temp table:
EXEC sp_rename '#OldTableName', '#NewTableName'Conclusion
Temp tables are a powerful tool for data manipulation in SQL Server. They offer temporary storage of data, improved performance in complex queries and procedures, and reduced table locking and blocking. By following the steps outlined in this guide, you can create, insert data into, and query temp tables like a pro. Happy coding!