Control flow statements, including IF-ELSE and WHILE loops, are valuable tools in Microsoft SQL Server for executing conditional logic and iterative processes within SQL queries. In this chapter, we'll explore the usage of IF-ELSE statements, WHILE loops, and their real-world applications.
Notes
Chapter 23: Variables in Microsoft SQL Server
Variables in Microsoft SQL Server allow you to store and manipulate data within a query or batch of queries. In this chapter, we'll explore the declaration and usage of variables, real-world applications, and provide examples.
1. Declaring and Using Variables
Declaring Variables:
Example :
Declaring a variable
DECLARE
@UserName
NVARCHAR(50)
In this example, we declare a variable named @UserName of type NVARCHAR(50).
Using Variables in Queries:
Example :
Using Variables in Queries:
SELECT
*
FROM
Employees
WHERE
EmployeeName=@UserName
In this query, we use the variable @UserName to filter the results.
2. Real-world Variable Usage
Dynamic Queries:
- Search Filters: Use variables to build dynamic search queries where users can input search criteria.
- Report Generation: Generate customized reports with variables for parameters such as date ranges or regions.
Data Validation:
- Input Validation: Store and validate user input in variables before processing to prevent SQL injection and ensure data integrity.
- Data Transformation: Perform data transformations on variables before inserting or updating records.
3.Key Takeaways
- Variables in SQL Server allow you to store and manipulate data within queries.
- They are declared using the DECLARE statement, assigned values using SET, and used in queries to parameterize data.
- Real-world applications of variables include dynamic queries, input validation, and data transformation.
4.Exercise Questions
- Create a SQL script that uses variables to filter products by a specified price range (minimum and maximum prices).
- Develop a dynamic query that retrieves orders placed within a specified date range provided as variables.
- Use a variable to store a user's email address and update their account information with a new email address.
- Write a script that accepts user input for a product name and uses a variable to search for products matching the input.
- Explain the advantages of using variables in SQL Server for dynamic queries and data validation.
- Discuss potential performance considerations when using variables in SQL, especially in scenarios involving complex queries and large datasets.
Stored Procedures in Microsoft SQL Server are precompiled SQL statements that can be executed with a single command. In this chapter, we'll explore the creation and usage of stored procedures, their advantages, and real-world applications.