Hello and welcome to this comprehensive guide on the case statement in SQL Server. In this article, we will take an in-depth look at the case statement, its syntax, and how it can be used in SQL Server. Whether you are a beginner or an experienced SQL Server user, this article is for you. So, let’s get started!
What is a Case Statement in SQL Server?
A case statement is a conditional expression in SQL Server that allows you to test whether an expression meets certain conditions and return different values depending on the outcome. It is typically used in select, update, and insert statements to manipulate data based on certain conditions.
Syntax of a Case Statement
The syntax of a case statement in SQL Server is as follows:
| Expression | Description |
|---|---|
| CASE | Starts the case statement |
| WHEN condition THEN result | Tests the condition and returns the result if it is true |
| ELSE result | Returns the result if none of the conditions are true |
| END | Ends the case statement |
The case statement can be used in different ways depending on your requirements. Let’s take a look at some examples.
Using a Case Statement in SQL Server
Example 1: Using a Simple Case Statement
Let’s say we have a table called “Students” with the following columns: “Name”, “Age”, and “Gender”. We want to return the gender of each student as “Male” or “Female”. We can use a simple case statement to achieve this:
SELECT Name, Age,
CASE Gender
WHEN 'M' THEN 'Male'
WHEN 'F' THEN 'Female'
ELSE 'Unknown'
END AS Gender
FROM Students
In this example, we are using a simple case statement to test the value of the “Gender” column. If the value is ‘M’, it returns ‘Male’. If the value is ‘F’, it returns ‘Female’. If the value is neither ‘M’ nor ‘F’, it returns ‘Unknown’.
Example 2: Using a Searched Case Statement
Let’s say we have a table called “Orders” with the following columns: “OrderID”, “ProductID”, “Quantity”, and “Price”. We want to calculate the total cost of each order by multiplying the quantity by the price. We can use a searched case statement to achieve this:
SELECT OrderID, ProductID, Quantity, Price,
CASE
WHEN Quantity > 10 AND Price > 50 THEN Quantity * Price * 0.9
WHEN Quantity > 5 AND Price > 30 THEN Quantity * Price * 0.95
ELSE Quantity * Price
END AS TotalCost
FROM Orders
In this example, we are using a searched case statement to test two conditions: if the quantity is greater than 10 and the price is greater than 50, it applies a 10% discount. If the quantity is greater than 5 and the price is greater than 30, it applies a 5% discount. If neither condition is met, it returns the regular total cost.
Example 3: Using a Nested Case Statement
Let’s say we have a table called “Employees” with the following columns: “EmployeeID”, “FirstName”, “LastName”, and “Salary”. We want to group employees into different salary brackets based on their salary. We can use a nested case statement to achieve this:
SELECT EmployeeID, FirstName, LastName, Salary,
CASE
WHEN Salary > 100000 THEN 'High'
WHEN Salary > 50000 THEN 'Medium'
WHEN Salary > 0 THEN 'Low'
ELSE 'Unknown'
END AS SalaryBracket,
CASE
WHEN Salary > 100000 THEN 'A'
WHEN Salary > 50000 THEN 'B'
WHEN Salary > 0 THEN 'C'
ELSE 'Unknown'
END AS Grade
FROM Employees
In this example, we are using a nested case statement to group employees into different salary brackets based on their salary. We are also using another nested case statement to assign a grade to each employee based on their salary.
Frequently Asked Questions
Q1. What is the difference between a simple case statement and a searched case statement?
A simple case statement tests a single value against multiple possible values, whereas a searched case statement tests multiple conditions against a single value.
Q2. Can I use a case statement in an update statement?
Yes, you can use a case statement in an update statement to modify data based on certain conditions.
Q3. Can I use a case statement in a where clause?
Yes, you can use a case statement in a where clause to filter data based on certain conditions.
Q4. Can I use a case statement in a join?
Yes, you can use a case statement in a join to join tables based on certain conditions.
Q5. Can I nest case statements?
Yes, you can nest case statements to achieve more complex conditional logic.
Conclusion
The case statement is a powerful conditional expression in SQL Server that allows you to manipulate data based on certain conditions. Whether you need to test a single value against multiple possible values or multiple conditions against a single value, the case statement can help you achieve your objectives. We hope this comprehensive guide has been helpful to you, and feel free to refer to it whenever you need to use a case statement in SQL Server.