SELECT query with a variable number of columns for each row - mysql

Question

I created a table of employees. Some of those employees report to other employees defined in the same table. Let's call them managers.
CREATE TABLE employees (
id INT PRIMARY KEY,
name VARCHAR(255) NOT NULL UNIQUE,
managerID INT NULL,
FOREIGN KEY (managerID) REFERENCES employees (id) ON DELETE RESTRICT
) ENGINE=INNODB;
Then, some values are entered in the database:
INSERT INTO employees(id, name, managerID)
VALUES (1, "Ivan", NULL),
(2, "Peter", 1),
(3, "Alexandra", 1),
(4, "Maria", 2),
(5, "Marian", 2),
(6, "Margarita", 3),
(7, "Mihail", 3),
(8, "Eva", 6);
I want a SELECT query which returns all employees and all the managers they report to. For now the next best thing I have is this:
SELECT employee.name AS Name, manager.name AS `Reports to:`
FROM employees,
LEFT JOIN employees AS manager ON employee.managerID = manager.id;
Which has predictable output:
Employee Reports to:
Ivan NULL
Peter Ivan
Alexandra Ivan
Maria Peter
Marian Peter
Margarita Alexandra
Mihail Alexandra
Eva Margarita
What I want is a such SELECT query that will return a variable number of columns based on the fact how many managers a single employee has. It's apparent to me that a recursive SELF JOIN will be required, but I don't know how to tell the DBMS I want a variable number of columns for each row and I don't know how to phrase the condition.
Desired output:

Answer 1

I understand that you want to generate a resultset where each record corresponds to an employee, with columns that show all managers of that employee (manager of the employee, then manager of the manager, etc...).
The thing to keep in mind is that a SQL query must return a fixed set of columns. The RDBMS needs to know in advance how many columns will be returned by the query to be able to parse it and execute it.
Here is a solution that can handle up to 5 levels of management. It workds by extending your logic with more LEFT JOINs. It's not pretty, but it works. You can add mor joins to handle more management levels.
SELECT
e0.name AS Name,
e1.name AS Manager1,
e2.name AS Manager2,
e3.name AS Manager3,
e4.name AS Manager4,
e5.name AS Manager5
FROM employees e0
LEFT JOIN employees e1 ON e1.id = e0.managerID
LEFT JOIN employees e2 ON e2.id = e1.managerID
LEFT JOIN employees e3 ON e3.id = e2.managerID
LEFT JOIN employees e4 ON e4.id = e3.managerID
LEFT JOIN employees e5 ON e5.id = e5.managerID
In this DB Fiddle with your sample data, the query returns:
| Name | Manager1 | Manager2 | Manager3 | Manager4 | Manager5 |
| --------- | --------- | --------- | -------- | -------- | -------- |
| Ivan | | | | | |
| Peter | Ivan | | | | |
| Alexandra | Ivan | | | | |
| Maria | Peter | Ivan | | | |
| Marian | Peter | Ivan | | | |
| Margarita | Alexandra | Ivan | | | |
| Mihail | Alexandra | Ivan | | | |
| Eva | Margarita | Alexandra | Ivan | | |