MySQL · December 20, 2023

MySQL Command: ITERATE

MySQL Command: ITERATE

MySQL is a popular open-source relational database management system that provides a wide range of powerful commands and functions. One such command is ITERATE, which allows you to iterate over a set of rows in a loop-like fashion. In this article, we will explore the ITERATE command and its usage in MySQL.

What is ITERATE?

The ITERATE command is used in conjunction with the LOOP statement to iterate over a set of rows returned by a SELECT query. It allows you to perform certain operations on each row of the result set. The basic syntax of the ITERATE command is as follows:

ITERATE label_name;

Here, label_name is an optional label that is used to identify the loop. If no label is specified, the ITERATE command will apply to the innermost loop.

How to Use ITERATE?

To use the ITERATE command, you need to follow these steps:

  1. Start by declaring a label for the loop using the DECLARE statement. For example:
DECLARE loop_label INT DEFAULT 1;
  1. Use the LOOP statement to define the loop. For example:
LOOP
  -- Perform operations on each row
  -- Use the ITERATE command to move to the next row
  ITERATE loop_label;
END LOOP;

Within the loop, you can perform various operations on each row of the result set. The ITERATE command is used to move to the next row and continue the loop until all rows have been processed.

Example Usage

Let's consider an example to understand the usage of the ITERATE command. Suppose we have a table named "employees" with the following structure:

+----+----------+-----------+
| id | name     | salary    |
+----+----------+-----------+
| 1  | John     | 5000      |
| 2  | Jane     | 6000      |
| 3  | Michael  | 5500      |
+----+----------+-----------+

We want to increase the salary of each employee by 10%. We can achieve this using the ITERATE command as follows:

DECLARE loop_label INT DEFAULT 1;
DECLARE current_salary INT;

LOOP
  SELECT salary INTO current_salary FROM employees WHERE id = loop_label;
  IF current_salary IS NULL THEN
    LEAVE;
  END IF;
  
  SET current_salary = current_salary * 1.1;
  
  UPDATE employees SET salary = current_salary WHERE id = loop_label;
  
  ITERATE loop_label;
  
  SET loop_label = loop_label + 1;
END LOOP;

In this example, we declare a label named "loop_label" and initialize it to 1. We then use the LOOP statement to define the loop. Inside the loop, we select the salary of the employee with the corresponding ID and store it in the "current_salary" variable. We check if the salary is null, and if so, we exit the loop using the LEAVE statement. Otherwise, we increase the salary by 10% and update the table with the new salary. Finally, we use the ITERATE command to move to the next row and continue the loop until all employees have been processed.

Summary

The ITERATE command in MySQL is a powerful tool for iterating over a set of rows returned by a SELECT query. It allows you to perform operations on each row and move to the next row using the ITERATE command. By using the ITERATE command in conjunction with the LOOP statement, you can efficiently process large result sets and perform complex operations on each row.

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