Understanding Case Statement in SQL Server

Hello Dev, welcome to this comprehensive guide on Case Statement in SQL Server. A Case Statement is a conditional statement that allows you to control the flow of your SQL queries based on certain conditions. This statement is one of the most important components of SQL that you need to master to become a successful developer. In this article, we will cover everything you need to know about Case Statement in SQL Server.

What is Case Statement in SQL Server?

Case Statement is a conditional statement used in SQL queries to control the flow of data based on certain conditions. It allows you to define specific actions or values for each condition, making your queries more efficient and targeted. With Case Statement, you can avoid writing repetitive queries and instead specify the desired result based on the input values.

SQL Server’s Case Statement comes in two forms, namely Simple Case Statement and Searched Case Statement. The Simple Case Statement checks the values of a single column or expression, while the Searched Case Statement checks multiple conditions to determine the appropriate action to take.

Simple Case Statement

The Simple Case Statement checks a single column or expression to determine the appropriate action to take. Here’s the syntax:

Code	Description
CASE expression	The expression to be evaluated
WHEN value1 THEN result1	The first condition and its result
WHEN value2 THEN result2	The second condition and its result
ELSE result	The result for all other values
END	Ends the statement

Let’s take a look at an example:

SELECTProductName,ProductPrice,CASE ProductPriceWHEN 10 THEN 'Cheap'WHEN 20 THEN 'Moderate'ELSE 'Expensive'END AS PriceRangeFROMProducts

In this example, we are checking the ProductPrice column for its value. If the value is 10, the result will be ‘Cheap’, if the value is 20, the result will be ‘Moderate’, and for all other values, the result will be ‘Expensive’.

Searched Case Statement

The Searched Case Statement checks multiple conditions to determine the appropriate action to take. Here’s the syntax:

Code	Description
CASE	The start of the statement
WHEN condition1 THEN result1	The first condition and its result
WHEN condition2 THEN result2	The second condition and its result
ELSE result	The result for all other conditions
END	Ends the statement

Let’s take a look at an example:

SELECTProductName,QuantityInStock,CASEWHEN QuantityInStock < 10 THEN 'Low Stock'WHEN QuantityInStock > 50 THEN 'High Stock'ELSE 'Medium Stock'END AS StockLevelFROMProducts

In this example, we are checking the value of QuantityInStock. If the value is less than 10, the result will be ‘Low Stock’, if the value is more than 50, the result will be ‘High Stock’, and for all other values, the result will be ‘Medium Stock’.

FAQs

What is the difference between Simple and Searched Case Statements?

The Simple Case Statement checks a single column or expression, while the Searched Case Statement checks multiple conditions to determine the appropriate action to take.

Can I nest Case Statements?

Yes, you can nest Case Statements within each other to create more complex queries.

What happens if no conditions are met in the Searched Case Statement?

If no conditions are met, the ELSE result will be returned.

Can I use Case Statements in WHERE clauses?

No, you cannot use Case Statements in WHERE clauses. They are only used in SELECT and ORDER BY clauses.

Is it possible to use Case Statements with GROUP BY clauses?

Yes, you can use Case Statements in GROUP BY clauses to group data based on specific conditions.

Conclusion

Case Statement is an essential component of SQL Server that allows you to control the flow of your queries based on specific conditions. With this statement, you can create more efficient and targeted queries that return the desired results. By mastering the Simple and Searched Case Statements, you can take your SQL skills to the next level.