Returning Query from PL/pgSQL - sql

Question

I have a list of records which has employee ids for each employee (emp_id), and their manager's employee id (manager_id)
Lets say I wanted to run a query to get all columns for the entire chain of command for Sandrine (emp_id = 63679) (i.e. Sandrine, Sandrine's boss, Sandrine's boss's boss, etc.)
How would I write this query?
I tried the following loop in PL/pgSQL:
CREATE FUNCTION getpersons() RETURNS SETOF person
LANGUAGE plpgsql AS
$$ Declare
counter INTEGER := 63679 ;
Begin
WHILE (Counter is not null) loop
RETURN QUERY EXECUTE (SELECT * FROM employees WHERE employees.emp_id = Counter);
Counter = employees.manager_id;
END LOOP;
END; $$
SELECT * from person;
the db looks like this:

Answer 1

Your function has several errors.
you are selecting from a table named employees, so the function should return setof employees, not "person"
You don't store the result of the select anywhere, so you can't actually assign the "counter" variable (which is a really bad choice for a variable name)
execute is only needed for dynamic SQL, not if you have static SQL
you should pass the ID of the employee to start with as a parameter, rather than hard coding it.
So in order to actually use the row you retrieved you need to store it in a variable, which can be defined as the same type as the resulting table.
Putting all of that together, your function should look like this:
CREATE FUNCTION getpersons(p_startid integer)
RETURNS SETOF employee
LANGUAGE plpgsql AS
$$ Declare
l_id INTEGER := p_startid;
l_row employee;
Begin
WHILE (l_id is not null) loop
SELECT *
into l_row
FROM employee
WHERE emp_id = l_id;
l_id := l_row.manager_id;
return next l_row;
END LOOP;
END;
$$
;
Then you can use it like this:
select *
from getpersons(63679);
However, it is not needed to write a function to traverse such a hierarchy. This can be done with a single SQL statement using a recursive common table expression
with recursive persons as (
select *
from employees
where id = 63679
union all
select ch.*
from employees ch
join persons p on p.manager_id = ch.id
)
select *
from persons;