plpgsql : how to reference variable in sql statement - postgresql

Question

I am rather new to PL/pgSQL and don't know how to reference a variable in a SELECT statement.
In this following function the SELECT INTO always returns NULL:
$body$
DECLARE
r RECORD;
c CURSOR FOR select name from t_people;
nb_bills integer;
BEGIN
OPEN c;
LOOP
FETCH c INTO r;
EXIT WHEN NOT FOUND;
RAISE NOTICE 'name found: %', r.name;
SELECT count(bill_id) INTO nb_bills from t_bills where name = r.name;
END LOOP;
END;
$body$
RAISE NOTICE allows me to verify that my CURSOR is working well: names are properly retrieved, but for some reason still unknown to me, not properly passed to the SELECT INTO statement.
For debugging purpose, I tried to replace the variable in SELECT INTO with a constant value and it worked:
SELECT count( bill_id) INTO nb_bills from t_bills where name = 'joe';
I don't know how to reference r.name in the SELECT INTO statement.
I tried r.name, I tried to create another variable containing quotes, it is always returning NULL.
I am stuck. If anyone knows ...

Answer 1

the SELECT INTO always returns NULL
not properly passed to the SELECT INTO statement.
it is always returning NULL.
None of this makes sense.
SELECT statements do not return anything by itself in PL/pgSQL. You have to either assign results to variables or explicitly return results with one of the available RETURN variants.
SELECT INTO is only used for variable assignment and does not return anything, either. Not to be confused with SELECT INTO in plain SQL - which is generally discouraged:
Combine two tables into a new one so that select rows from the other one are ignored
It's not clear what's supposed to be returned in your example. You did not disclose the return type of the function and you did not actually return anything.
Start by reading the chapter Returning From a Function in the manual.
Here are some related answers with examples:
Can I make a plpgsql function return an integer without using a variable?
Return a query from a function?
How to return multiple rows from PL/pgSQL function?
Return setof record (virtual table) from function
And there may be naming conflicts with parameter names. We can't tell unless you post the complete function definition.
Better approach
That said, explicit cursors are only actually needed on rare occasions. Typically, the implicit cursor of a FOR loop is simpler to handle and cheaper:
Truncating all tables in a Postgres database
And most of the time you don't even need any cursors or loops at all. Set-based solutions are typically simpler and faster.