How Temporary Table in MS SQL Enhances the Query Performance

Large datasets often involve complex calculations to generate accurate insights and reports. However, repeatedly running queries on the entire dataset can significantly slow down data processing operations. An effective strategy to manage this efficiently is to use temporary tables in MS SQL.

A temporary table in MS SQL serves as a temporary storage space. You can temporarily store data to process intermediate results without impacting the entire database. This enables you to carry out calculations efficiently and enhances query performance, reducing the load on the main database.

This article will elaborate on using SQL Server temporary table to enhance your organization’s operational efficiency.

What is a Temporary Table in MS SQL?

It is also known as a temp table, provides a convenient workspace for processing data within a batch or procedure, allowing the storage of intermediate results. Using MS SQL temp tables enhances query performance and helps manage data more effectively. 

Key Characteristics of MS SQL Temp Table

• Scope: The scope of a temporary table is limited to the session in which it is created; the tables are only accessible within the current batch or procedure running in the session.
• Flexibility: You can use a temp table in MS SQL in different scenarios. The tables can be used to share complex datasets between multiple stored procedures in the same session. You can also use temp tables to transfer read-only datasets from an application to SQL Server routines.
• Simplifying Queries: The temp tables in MS SQL help you break down complex SQL queries into smaller and manageable parts. By isolating different parts of a query into separate temporary tables, the overall SQL code becomes easier to understand. 

What Is TempDB in MS SQL?

TempDB is a system database in SQL Server that serves as a central storage repository for temporary data, objects, and temporary tables. The SQL Server uses TempDB on the compute node to store a temporary table for performing queries. You can use TempDB as a workspace for temporary storage while performing operations such as sorting, joining, and merging within a temp table.

TempDB also allows you to store row versions, which helps you track changes performed within a row. This helps with operations, including snapshot isolation levels, online indexing operations, and multiple active results sets, requiring transactional consistency.

Although you can dynamically manage the space in TempDB, there are issues related to space contention, version store overhead, and TempDB growth. To mitigate these issues, the SQL Server administrators must regularly monitor the usage space and configure the appropriate initial size and growth settings of TempDB Files.

Types of Temporary Tables in MS SQL 

MS SQL supports two types of temporary tables, both stored within a TempDB database. Let’s take a look at each type:

Local Temporary Table

A local temporary table in MS SQL is visible only to the session in which it is created. These tables store and process temporary data for a specific session. The local temporary table automatically drops when the session that created it is closed, or the query that created it is completed. You can perform different operations, such as create, insert, and delete, on the local temp table.

To create a local temporary table, you can use a single ‘#’ as the prefix before the table name. If the table is made within the stored procedure, it will be dropped automatically upon query completion.

Global Temporary Table

A global temporary table is an object created using a double ‘##’ sign as a prefix. You can access these tables from any session, allowing for the sharing of temporary data across multiple sessions.

In these sessions, you can use the global temp table to perform operations like inserting, deleting, or updating. This table remains available until the last session referencing it is closed.

How to Create a Temporary Table in MS SQL

Using the MS SQL create temp table syntax, and you can generate a workspace for storing temporary data to perform SQL operations.

Let’s look at the syntax:

To Create a Local Temporary Table:

CREATE TABLE #temptable (column1_name datatype, column2_name datatype); 

To Create a Global Temporary Table:

CREATE TABLE ##temptable (column1_name datatype, column2_name datatype);

An Example of Using a Temporary Table

Let’s assume your company had a successful sales quarter, and you want to reward your employees by adding a bonus of $1000 to their salaries. You can use a temporary table to do so:

Create a Temp Table for Employees:

CREATE TABLE #TempEmployees (

EmployeeID INT,

FirstName VARCHAR(50),

LastName VARCHAR(50),

HireDate DATE,

Salary INT

);

This code will create a temporary table called TempEmployees.

Insert Data into the Temp Table:

INSERT INTO #TempEmployees (EmployeeID, FirstName, LastName, HireDate, Salary) VALUES

(1, ‘XYZ’, ‘ABC’, ‘2024-06-24’, 12000),

(2, ‘WXY’, ’GDB’, ‘2023-11-20’, 10000),

(3, ‘RTD’, ‘EMS’, ‘2022-09-07’, 23000);

The above code will insert records into the TempEmployees table.

Query Temp Table:

SELECT * FROM #TempEmployees; 

You can use this code to select temporary table in SQL Server and view all the records inside it.

Update the Data in the Temp Table:

UPDATE #TempEmployees

SET Salary = Salary + 1000;

This code will update the salary of all the employees within the temp table named TempEmployees by adding a $1000 bonus.

Query Table After Modifications:

SELECT * FROM #TempEmployees;

This code will showcase the updated data in the temp table TempEmployees. 

DROP the Table:

DROP TABLE #TempEmployees; 

Once the modifications are done, you can drop the temp table in MS SQL and free up your resources.

Difference between MS SQL Temp Tables and Permanent Tables

Understanding the differences between temporary and permanent tables in MS SQL can help with effective data management. Here are some of the key differences: 

Factor	Temporary Table	Permanent Table
Lifespan	Exists only during the session in which it is created and is automatically dropped when the session ends.	Persists even beyond the session, remaining in the database until it is modified or deleted.
Storage Allocation	It is stored temporarily within a TempDB.	Allocated on a disk within a specific MS SQL database.
Syntax for Creation	When creating a local temporary table, you need to put the prefix ‘#’ before its name, and for the global temporary table, you must add a double ‘##’ sign as a prefix.	There is no specific prefix or character to add before the name when creating a permanent table in MS SQL.
Data Retention	The data is automatically deleted when the table is dropped at the end of a session.	The data remains until you explicitly delete or modify it.
Indexes and Constraints	Consists of indexes and constraints, which are also temporary and dropped when the table is dissolved.	Consists of indexes and constraints that persist and can be modified as needed.
Performance	It improves the query performance of your database by allowing you to process complex queries separately.	It improves your query performance by enabling long-term indexing, partitioning, and data compression.

Although temporary tables can be used to store and process intermediate data in MS SQL, it does not inherently provide a mechanism for data validation and quality checks. You can use integration tools to implement data transformation, cleaning, and validation before loading into temp tables.

How Hevo Helps in Maintaining Data Integrity Within MS SQL Temp Tables

Hevo is a near-real-time ELT data integration platform that helps you streamline data movement into MS SQL Server, including temp tables, through its no-code automated data pipeline. It offers 150+ data sources, including databases, data warehouses, and cloud platforms, from where you can quickly transfer data into your MS SQL temp tables.

Benefits of Using Hevo 

• Data Transformation:  Hevo offers two types of transformations: Python-based and drag-drop. These transformations allow you to clean and prepare your source data before loading it into MS SQL temp tables.
• Automated Data Mapping: The automated schema mapping feature of Hevo automatically reads and maps the source data schema into MS SQL temp tables. This helps you to maintain consistency in data formats and types.
• Incremental Data Loading: Hevo’s incremental data loading feature enables you to load recently modified data into your MS SQL temp tables; you don’t have to upload the entire dataset repeatedly. This ensures you can access current data for analytics and decision-making.

Use Cases of SQL Server Temporary Table

The temp tables in SQL are versatile and can be utilized in various scenarios. Here are some of the common use cases:

To Analyze Data Subsets

Temp tables serve as a sandbox for data analysis without impacting the integrity of your original database within SQL Server. You can use a temporary table to analyze specific data subsets. This allows you to test results and calculations on the subgroup to validate assumptions rather than modifying the original dataset.

For instance, you can create and use temp tables to analyze the sales performance of a specific product in different regions. You can copy the data from the main sales tables into temp tables and study what factors impact sales in specific areas without altering the main sales table.

Reduce Lock Contention

Due to frequent and lengthy operations, main tables could get locked, slowing down your processing operations. You can use a temp table to perform bulk operations and move only the final results to the main table, helping you minimize lock durations.

For instance, in a retail database, updates to inventory can cause lock retention issues. You can adjust inventory data using temp tables and merge the results in the main inventory table. This will help minimize lock duration and enhance overall performance.

Ad-hoc Analysis and Reporting

Ad-hoc analysis involves conducting on-the-fly queries to generate reports to answer specific business questions. You can use a temp table to analyze data for ad-hoc analysis without affecting the underlying databases.

For instance, to create a quarterly sales report, you can include data that needs to be covered in standard reports. You can use temp tables to query sales data for different quarters, including calculations for product profitability or regional sales performance. After analysis, you can summarize the data to generate one-off reports.

Conclusion

Using temporary MS SQL tables offers flexibility for storing, managing, and querying data. You can analyze specific data subsets to validate results without affecting your primary dataset. The temp tables also serve as effective staging areas for data transformation to handle inconsistencies in data before moving it to permanent storage. This data refinement improves data quality and enhances the analysis process, resulting in better decision-making.

Simplify the migration of temporary table in MS SQL with Hevo Data for easier query performance. Schedule a demo to know more.

FAQs

1. How is a temporary table different from an ordinary table? 

A temporary table exists for the session for which it is created. On the other hand, an ordinary table persists beyond the session and is stored in the SQL database for long-term use.

2. How do you drop a temporary table in MS SQL if it exists? 

IF OBJECT_ID('tempdb..#TempTableName') IS NOT NULL

    DROP TABLE #TempTableName;

The code first checks if the temp table exists in a TempDB database. If it does, the drop statement is executed.

3. When using the SELECT INTO command for temp tables, are results logged into the transaction log? 

In MS SQL Server, all user database operations, including those involving temporary tables, are logged. So when you use the SELECT INTO command, which creates a new table and populates it with data extracted from a query, the operation is logged in the transaction log.

4. Is there a record limit for temporary tables on the SQL Server? 

No, there is no specific record limit for temporary table in MS SQL Server. The capacity is limited by the available disk space in the TempDB database hosting these tables.