Case When SQL

How can I conditionally return different values based on conditions in SQL?

The CASE WHEN statement in SQL allows you to perform conditional logic within a query. It's a powerful tool for returning different values based on various conditions. It's crucial for creating dynamic and flexible queries.

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Description

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Example H3

The CASE WHEN statement is a fundamental SQL construct for conditional logic. It enables you to return different values based on the evaluation of conditions within a query. This is particularly useful for transforming data or creating calculated fields based on specific criteria. Imagine you have a table of customer orders, and you want to categorize them as 'High-Value', 'Medium-Value', or 'Low-Value' based on the order total. The CASE WHEN statement makes this straightforward. It's a versatile tool that can be used in SELECT, UPDATE, and other SQL statements. The basic structure involves a series of WHEN conditions followed by a THEN clause specifying the value to return if the condition is true. A final ELSE clause (optional) handles cases where none of the WHEN conditions are met. This allows for complex conditional logic within a single query, enhancing the flexibility and power of your SQL operations.

Why Case When SQL is important

The CASE WHEN statement is crucial for data manipulation and analysis. It allows for dynamic data transformations, enabling complex queries that adapt to various conditions. This flexibility is essential for reporting, data analysis, and creating custom business logic within SQL.

Case When SQL Example Usage


-- Sample table: Customers
CREATE TABLE Customers (
    CustomerID INT PRIMARY KEY,
    FirstName VARCHAR(50),
    LastName VARCHAR(50),
    OrderTotal DECIMAL(10, 2)
);

INSERT INTO Customers (CustomerID, FirstName, LastName, OrderTotal)
VALUES
(1, 'John', 'Doe', 100.00),
(2, 'Jane', 'Smith', 50.00),
(3, 'Peter', 'Jones', 200.00),
(4, 'Mary', 'Brown', 25.00);

-- Query to categorize orders
SELECT
    CustomerID,
    FirstName,
    LastName,
    OrderTotal,
    CASE
        WHEN OrderTotal > 150 THEN 'High-Value'
        WHEN OrderTotal BETWEEN 50 AND 150 THEN 'Medium-Value'
        ELSE 'Low-Value'
    END AS OrderCategory
FROM
    Customers;

Case When SQL Syntax

Common Mistakes

Forgetting the END keyword at the end of the CASE statement.
Using incorrect comparison operators (e.g., using = instead of <=> for NULL comparisons).
Omitting the ELSE clause, which can lead to unexpected results if no WHEN condition is met.

Frequently Asked Questions (FAQs)

How can I categorize order totals using a single SQL CASE WHEN statement?

You can embed multiple conditions in one CASE WHEN block to translate numeric order_total values into readable tiers. For example:
SELECT order_id, CASE WHEN order_total >= 1000 THEN 'High-Value' WHEN order_total >= 300 THEN 'Medium-Value' ELSE 'Low-Value' END AS order_tierFROM orders;
The database evaluates each WHEN clause in order and returns the corresponding label, eliminating the need for separate queries or temporary tables.

Is CASE WHEN limited to the SELECT clause, or can I use it in UPDATE statements too?

CASE WHEN is not just for result sets. You can embed it in UPDATE, INSERT, or even WHERE clauses to apply conditional logic during data modification. For instance, you might run:
UPDATE ordersSET shipping_priority = CASE WHEN order_total >= 1000 THEN 1 ELSE 2 END;
This single command updates every row according to its order_total, making bulk data transformations concise and performant.

How does Galaxy’s AI copilot accelerate writing complex CASE WHEN logic?

Galaxy’s context-aware AI copilot auto-completes column names, suggests CASE WHEN patterns, and even rewrites queries when your schema changes. Instead of typing repetitive WHEN/THEN clauses manually, you can prompt the copilot with “categorize orders by total” and receive a ready-to-run CASE statement inside the lightning-fast Galaxy editor—saving time and reducing syntax errors.