Explain the purpose of the MYSQL CASE statement

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The CASE statement in MySQL is a powerful control structure that allows you to perform conditional logic in SQL queries. It is similar to the IF-THEN-ELSE statement in other programming languages. The CASE statement is often used to create conditional output in the result set or to perform conditional operations on data during the query process.

Here's the basic syntax of the CASE statement:

sql code
CASEWHEN condition1 THEN result1 WHEN condition2 THEN result2 ... ELSE defaultResult END
  • condition1, condition2, etc.: These are the conditions that are evaluated in the order they appear. If a condition is true, the corresponding result is returned.
  • result1, result2, etc.: These are the values returned when the corresponding condition is true.
  • defaultResult: This is the value returned if none of the conditions are true (optional).

Example 1: Simple CASE Statement

Let's say you have a table orders with a column order_status. You want to categorize orders based on their status and assign a label. You can use a CASE statement for this:

sql code
SELECT order_id, order_status, CASEWHEN order_status ='shipped'THEN'Shipped'WHEN order_status ='processing'THEN'Processing'ELSE'Unknown'ENDAS status_label FROM orders;

In this example, the CASE statement checks the order_status column. If it's "shipped", it returns "Shipped". If it's "processing", it returns "Processing". If it's any other value, it returns "Unknown".

Example 2: Searched CASE Statement

You can also use a searched CASE statement, where each WHEN clause contains its own condition:

sql code
SELECT product_id, quantity, CASEWHEN quantity >10THEN'High demand'WHEN quantity >0THEN'In stock'ELSE'Out of stock'ENDAS stock_status FROM products;

In this example, the CASE statement checks the quantity column. If quantity is greater than 10, it returns "High demand". If it's greater than 0 but not more than 10, it returns "In stock". If it's 0 or less, it returns "Out of stock".

The CASE statement provides a way to customize the output of your queries based on specified conditions, making your SQL queries more flexible and expressive.

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