In SQL, various filtering and data fetching techniques are used to fetch interrelated searches or handle complex conditions. In this article, we will learn about CASE statements and how to implement Nested Cases in SQL.
What is a CASE Statement in SQL?
CASE statement creates a conditional space where the expected output data points are based on the given conditions. It is specifically useful for implementing conditional statements within queries, to get a flexible reach around the data.
Being such a valuable asset to database management systems, CASE statements also allow the transformation of data. They evaluate every condition until they have reached a point where the condition is met allowing the generation of a suitable output.
CASE statements can be used for multiple operations such as performing search filters, handling NULL values, sorting based on custom conditions, transforming data, and deriving columns.
Types of CASE Statement
Case statements are a powerful tool, it is important to understand how different types of CASE statements can be used. It is essential to understand the method and order of execution for CASE statements to avoid errors.
1) Simple CASE Statements in SQL
The Simple CASE statements are used to check and compare whether the given condition matches with the specified value to give an expected output to the user. It allows the creation of structured data.
WHEN value1 THEN outcome1
WHEN value2 THEN outcome2
END AS alias_name
Let us understand the use of Simple CASE Statements in SQL with an example.
In the above example, we have used CASE statements to categorize the SaleAmount into ‘High Value’, ‘Medium Value’, and ‘Low Value’.
2) Aggregation using CASE Statements in SQL
SQL CASE statements allow aggregational functions to operate with conditional logic. This is often useful when we want to perform some operations on a dataset to get a derived column while considering different cases.
WHEN condition1 THEN outcome1
WHEN condition2 THEN outcome2
END) AS result_alias
Let us understand aggregation in CASE statements through an example
In the above example, we have used the COUNT aggregation to count the number of high-valued, Medium-valued, and low-valued airplanes based on their SalesAmount.
3) Nested Query Statements in SQL using CASE
Nested queries are one of the advanced methods used in CASE Statements to dive deeper into data with multidimensional features. It allows the user to apply a condition over a condition allowing an in-depth analysis. It tailors the data based on complex and interrelated conditions.
Various multiple conditional statements can be applied over the basic block of conditions. These blocks of statements test themselves on the given specification before moving out towards other outer queries.
WHEN condition1 THEN
WHEN nested_condition1 THEN nested_result1
WHEN nested_condition2 THEN nested_result2
WHEN condition2 THEN result2
END AS alias_name
Let us understand the use of Nested Queries in CASE statements through an example
In the above example, we have used multiple nested statements to categorize the type of customer as well as the type of discount given to the customer.
How to Apply a Nested CASE?
In SQL, the CASE statements function works just like the if-else statements, with each block of the CASE statement testing itself individually. Here's how they operate:
- Start by identifying the innermost condition where the test is to be applied.
- Give the values and their corresponding actions for both the true and false results of the condition.
- End the innermost CASE statement. If the innermost condition comes out to be false, then the system generally proceeds to the next outer query.
- The outer query then tests its condition, and the process repeats.
- It then continues testing outward through nested CASE statements until reaching the outermost query and ending the overall set of CASE statements.
What is the alternative to nested CASE in SQL?
Alternative ways to apply the nested CASE statements in SQL may involve the use of conditional functions such as IIF(), SWITCH(), and CHOOSE(). We can also consider using stored procedures and user-defined functions as alternatives, as these can improve code efficiency.
Overall in this article, we looked at various types of case statements and also focused on how nested cases in SQL. With the use of various examples, we were able to identify the workflow of these CASE statements gaining insights into their application and use cases. If you want to know more about them, connect with a professional SQL Tutor online anytime.