mysql loop with code examples

MySQL is an open-source relational database management system, which means it facilitates the storage, organization, and management of data. It is designed to be scalable, able to handle small, medium, and large datasets. One of the most important components of any database system is the ability to manipulate the data stored in it. Loops are an essential part of any programming language, and MySQL is no exception. In this article, we will introduce you to MySQL loops with various code examples.

What are loops in MySQL?

In programming, a loop is a block of code that executes repeatedly until a specified condition is met. Loops make it possible to perform repetitive tasks until a certain condition is achieved. They help reduce unnecessary code and increase efficiency while programming. MySQL supports several types of loops:

While loop:

The while loop executes a set of code as long as a specified condition evaluates to true. In MySQL, the syntax for the while loop is as follows:

WHILE condition DO
   statement;
END WHILE;

Here's an example of a while loop in MySQL that prints numbers from 1 to 10:

DECLARE i INT DEFAULT 1;
WHILE i <= 10 DO
  SELECT i;
  SET i = i + 1;
END WHILE;

The above code will output:

Repeat-Until loop:

The Repeat-Until loop executes a set of code repeatedly until a specified condition evaluates to true. In MySQL, the syntax of Repeat-Until loop is as follows:

REPEAT
   statement;
UNTIL condition END REPEAT;

Here's an example of the repeat-until loop that prints numbers from 1 to 10:

DECLARE i INT DEFAULT 1;
REPEAT
  SELECT i;
  SET i = i + 1;
UNTIL i > 10 END REPEAT;

The above code will output:

For loop:

The For loop is used to iterate a block of code for a specified number of times. In MySQL, the syntax for the for loop is as follows:

FOR var_counter IN [REVERSE] start_value..end_value
   statement;
END FOR;

Here's an example of a for loop that prints the even numbers from 2 to 10:

FOR i IN 2..10 BY 2 DO
  SELECT i;
END FOR;

The above code will output:

Cursors for looping through result sets:

MySQL also provides cursors for looping through result sets. Cursors are often used in stored procedures to execute logic over a number of rows of data.

Here's an example of a cursor that loops through a result set and increments the salary of employees by 10%:

DELIMITER $$
 
CREATE PROCEDURE update_salary()
BEGIN
  DECLARE emp_id INT;
  DECLARE salary DECIMAL(10,2);
  DECLARE done INT DEFAULT FALSE;
 
  -- Declare a cursor to fetch employee details
  DECLARE emp_cursor CURSOR FOR SELECT id, salary FROM employees WHERE department = 'Sales';
 
  -- Declare a 'NOT FOUND' handler
  DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = TRUE;
 
  -- Open the cursor and fetch the employee details
  OPEN emp_cursor;
 
  cursor_loop: LOOP
    -- Fetch the next row into variables
    FETCH emp_cursor INTO emp_id, salary;
    IF done THEN
      LEAVE cursor_loop;
    END IF;
    
    -- Update the salary by 10%
    UPDATE employees SET salary = salary * 1.10 WHERE id = emp_id;
  END LOOP;
 
  -- Close the cursor
  CLOSE emp_cursor;
 
END$$
 
DELIMITER ;

In the above example, we create a stored procedure named update_salary that declares a cursor that selects employees from the Sales department. We then open the cursor and loop through the result set until there are no more rows to fetch. Inside the loop, we increment the salary of each employee by 10%.

Conclusion

In conclusion, loops are an essential component of any programming language and are no different in MySQL. Loops make it possible to perform repetitive tasks with ease and efficiency, and MySQL supports several types of loops, including while, repeat-until, for, and cursors for looping through result sets. With the various examples provided in this article, you should now have a better understanding of how to implement loops in MySQL.

let's dive deeper into some of the concepts and code examples mentioned in the previous article.

While loop in MySQL:

The while loop is one of the basic looping constructs in MySQL. A while loop is used when we need to execute a block of code repeatedly based on a condition. The loop will execute until the condition is false.

Let's consider the following example:

DECLARE i INT DEFAULT 1;
WHILE i <= 5 DO
   SELECT i;
   SET i = i + 1;
END WHILE;

In the above while loop, we have declared a variable 'i' and initialized it with 1. The loop will continue to execute until the 'i' variable becomes greater than 5. Inside the loop, the SELECT statement is used to display the value of the 'i' variable, and then we are incrementing the value of variable 'i' by 1 at the end of each iteration.

The output of the above code will be:

Repeat-Until loop in MySQL:

The Repeat-Until loop in MySQL is similar to a while loop, but the condition is checked at the end of the loop instead of at the beginning. The loop will execute at least once, even if the condition is false.

DECLARE i INT DEFAULT 5;

REPEAT
   SELECT i;
   SET i = i - 1;
UNTIL i = 1 END REPEAT;

In the above repeat-until loop, we have initialized the 'i' variable with 5. Inside the loop, we are displaying the value of variable 'i' using the SELECT statement, and then we are decrementing the value of the 'i' variable by 1 at the end of each iteration. The loop will continue to execute until the value of 'i' becomes 1.

The output of the above code will be:

For loop in MySQL:

The for loop is another popular looping construct in MySQL, and it is used when we need to execute a block of code for a fixed number of times.

Consider the following example:

FOR i IN 1..5 DO
   SELECT i;
END FOR;

In the above for loop, we are iterating through a range of values starting from 1 and ending at 5. Inside the loop, we are displaying the value of variable 'i' using the SELECT statement.

The output of the above code will be:

Cursors for looping through result sets:

MySQL cursors are used to loop through a set of rows returned by a SELECT statement. Cursors are often used in stored procedures to execute logic over a number of rows of data.

Consider the following example:

DELIMITER $$

CREATE PROCEDURE display_customers()
BEGIN
   DECLARE done INT DEFAULT FALSE;
   DECLARE cust_id INT;
   DECLARE cust_name VARCHAR(50);
   DECLARE cur CURSOR FOR SELECT id, name FROM customers;
   DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = TRUE;

   OPEN cur;

   loop_label: LOOP
      FETCH cur INTO cust_id, cust_name;
      IF done THEN
         LEAVE loop_label;
      END IF;
    
      SELECT CONCAT(cust_id, ' - ', cust_name);
   END LOOP;

   CLOSE cur;

END$$

In the above example, we are creating a stored procedure named display_customers. Inside the stored procedure, we are declaring variables for customer Id and customer name. We then use a SELECT statement to fetch the rows from the customers table and store them in a cursor. Next, we use the FETCH statement to fetch the rows of data and store them in the variables. Finally, we use the SELECT statement to display the customer id and name.

The output of the above code will be the list of all customers from the customers' table.

Conclusion:

In this article, we learned about MySQL loops and how they work. We also discussed different loop constructs in MySQL, such as the while loop, repeat-until loop, for loop, and Cursors. The article provided various examples of each loop construct to help you better understand how they work in specific scenarios. Loops are essential in programming, and with the knowledge gained through this article, you can now use them effectively in MySQL to write efficient and optimized code.

mysql loop with code examples

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Ahmed Zakaria

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Ahmed Zakaria

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