sql while loop

Galaxy Glossary

How can I repeat a block of SQL code multiple times based on a condition?

SQL doesn't have a direct `WHILE` loop like some programming languages. Instead, you can achieve repeated execution using `WHILE` loops within stored procedures or by combining `WHILE` loops with `cursors`. This allows you to iterate through data and perform actions based on conditions.

Thank you! Your submission has been received!

Oops! Something went wrong while submitting the form.

Description

SQL, unlike procedural languages like Python or Java, doesn't have built-in `WHILE` loops for directly iterating through data. While you can't use a `WHILE` loop directly within a standard SQL query, you can achieve similar functionality using stored procedures and cursors. Stored procedures allow you to encapsulate a series of SQL statements, including conditional logic. A cursor acts as a pointer to a result set, enabling you to fetch rows one by one and perform operations on them. This approach is often used when you need to process data row by row, update multiple rows based on a condition, or perform complex calculations on a dataset.

Why sql while loop is important

Stored procedures and cursors, while not direct `WHILE` loops, are crucial for automating complex data manipulation tasks. They improve code organization, reusability, and security by encapsulating logic within the database.

Example Usage

```sql -- Stored procedure to update product prices based on a condition CREATE PROCEDURE UpdateProductPrices() BEGIN DECLARE done INT DEFAULT FALSE; DECLARE product_id INT; DECLARE product_price DECIMAL(10, 2); DECLARE price_cursor CURSOR FOR SELECT product_id, price FROM products WHERE price < 10; DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = TRUE; OPEN price_cursor; read_loop: LOOP FETCH price_cursor INTO product_id, product_price; IF done THEN LEAVE read_loop; END IF; UPDATE products SET price = price * 1.10 WHERE product_id = product_id; END LOOP; CLOSE price_cursor; END; CALL UpdateProductPrices(); SELECT * FROM products; ```

Common Mistakes

Trying to use a `WHILE` loop directly within a standard SQL query.
Incorrectly using `FETCH` statements within the cursor loop.
Forgetting to `CLOSE` the cursor after use.
Failing to handle the `NOT FOUND` condition in the cursor loop.

Want to learn about other SQL terms?