Welcome, Dev! If you’re interested in learning more about SQL Server Case Then, you’re in the right place. In this article, we’ll cover everything you need to know about this handy SQL function. From basic syntax to advanced examples, we’ll guide you through it all. So, let’s dive in!
What is SQL Server Case Then?
Before we get into the nitty-gritty of SQL Server Case Then, let’s first define what it is. In simple terms, Case Then is a conditional statement in SQL. It allows you to execute different portions of code based on certain conditions. This is particularly useful when you need to perform different actions based on different conditions.
In SQL Server, the Case Then statement consists of two main parts: the Case expression and the Then expression. The Case expression defines the condition that needs to be evaluated, while the Then expression defines the action that needs to be taken if the condition is met.
Basic Syntax of SQL Server Case Then
The basic syntax of SQL Server Case Then looks like this:
SELECTColumn1,Column2,CASEWHEN Condition1 THEN Result1WHEN Condition2 THEN Result2ELSE DefaultResultEND AS NewColumnFROMTableName
Let’s take a closer look at each part of the statement:
- SELECT: This is the standard SQL command used to select columns from a table.
- Column1, Column2: These are the columns you want to select from the table.
- CASE: This is the start of the Case Then statement.
- WHEN Condition1 THEN Result1: This is where you define the first condition that needs to be evaluated. If the condition is met, the code in Result1 will be executed.
- WHEN Condition2 THEN Result2: This is where you define the second condition that needs to be evaluated. If the condition is met, the code in Result2 will be executed.
- ELSE DefaultResult: This is the default result that will be executed if none of the conditions are met.
- END AS NewColumn: This is where you define the new column name for the output.
- FROM TableName: This is the name of the table you’re selecting data from.
Example of SQL Server Case Then
Let’s look at an example of SQL Server Case Then in action:
EmployeeID |
EmployeeName |
Salary |
Bonus |
|---|---|---|---|
1 |
John |
50000 |
10000 |
2 |
Jane |
60000 |
12000 |
3 |
Bob |
70000 |
14000 |
SELECTEmployeeName,Salary,CASEWHEN Salary > 60000 THEN 'High'WHEN Salary > 50000 THEN 'Medium'ELSE 'Low'END AS SalaryRangeFROMEmployeeTable
In this example, we’re selecting the EmployeeName and Salary columns from the EmployeeTable. We also add a new column called SalaryRange using the Case Then statement. If the Salary is greater than 60000, the value in the SalaryRange column will be ‘High’. If the Salary is greater than 50000, the value in the SalaryRange column will be ‘Medium’. Otherwise, the value in the SalaryRange column will be ‘Low’.
EmployeeName |
Salary |
SalaryRange |
|---|---|---|
John |
50000 |
Low |
Jane |
60000 |
Medium |
Bob |
70000 |
High |
Advanced Examples of SQL Server Case Then
Using Case Then with Joins
You can also use SQL Server Case Then with joins to create more complex queries. Let’s look at an example:
EmployeeID |
EmployeeName |
DepartmentID |
DepartmentName |
|---|---|---|---|
1 |
John |
1 |
Sales |
2 |
Jane |
2 |
Marketing |
3 |
Bob |
2 |
Marketing |
SELECTEmployeeName,DepartmentName,CASEWHEN DepartmentName = 'Sales' THEN 'Sales Department'ELSE 'Other Department'END AS DepartmentTypeFROMEmployeeTableJOIN DepartmentTable ON EmployeeTable.DepartmentID = DepartmentTable.DepartmentID
In this example, we’re selecting the EmployeeName, DepartmentName, and DepartmentType columns from the EmployeeTable and the DepartmentTable using a join. We’re using the Case Then statement to create a new column called DepartmentType. If the DepartmentName is ‘Sales’, the value in the DepartmentType column will be ‘Sales Department’. Otherwise, the value in the DepartmentType column will be ‘Other Department’.
EmployeeName |
DepartmentName |
DepartmentType |
|---|---|---|
John |
Sales |
Sales Department |
Jane |
Marketing |
Other Department |
Bob |
Marketing |
Other Department |
Using Case Then with Multiple Conditions
You can also use SQL Server Case Then with multiple conditions. Let’s look at an example:
EmployeeID |
EmployeeName |
DepartmentID |
Salary |
|---|---|---|---|
1 |
John |
1 |
50000 |
2 |
Jane |
2 |
60000 |
3 |
Bob |
2 |
70000 |
SELECTEmployeeName,CASEWHEN DepartmentID = 1 AND Salary > 40000 THEN 'Sales Department'WHEN DepartmentID = 2 AND Salary > 50000 THEN 'Marketing Department'ELSE 'Other Department'END AS DepartmentTypeFROMEmployeeTable
In this example, we’re selecting the EmployeeName and DepartmentType columns from the EmployeeTable. We’re using the Case Then statement to create a new column called DepartmentType. If the DepartmentID is 1 and the Salary is greater than 40000, the value in the DepartmentType column will be ‘Sales Department’. If the DepartmentID is 2 and the Salary is greater than 50000, the value in the DepartmentType column will be ‘Marketing Department’. Otherwise, the value in the DepartmentType column will be ‘Other Department’.
EmployeeName |
DepartmentType |
|---|---|
John |
Sales Department |
Jane |
Marketing Department |
Bob |
Marketing Department |
FAQs about SQL Server Case Then
What is the difference between Case When and Case Then?
There is no difference between Case When and Case Then. Case Then is simply a more intuitive way of representing the SQL Case statement.
Can I use multiple Case Then statements in a single query?
Yes, you can use multiple Case Then statements in a single query. Just make sure to separate them with commas.
Can I use Case Then in a WHERE clause?
No, you cannot use Case Then in a WHERE clause. The WHERE clause only accepts conditions, not expressions or statements.
Can I use Case Then with NULL values?
Yes, you can use Case Then with NULL values. You can define a separate condition for NULL values using the IS NULL or IS NOT NULL operators.
Can I nest Case Then statements?
Yes, you can nest Case Then statements to create more complex expressions. Just make sure to keep track of the syntax and the order of the statements.
Conclusion
SQL Server Case Then is a powerful function that allows you to perform conditional statements in SQL. It’s a useful tool for creating complex queries and reports that require different actions based on different conditions. By mastering the basic syntax and examples of Case Then, you can take your SQL skills to the next level. We hope this guide has been helpful for you, Dev!