PL/pgSQL control structures for lists / arrays

问题

Is it possible to use something like this in Postgres? This is the example from PL/SQL what I want to do:

PROCEDURE CREATE_PAYMENT(P_AMOUNT IN NUMBER,
                         P_INVOICE_LIST IN SIMPLEARRAYTYPE, 
                         P_AMOUNT_LIST IN NUMBER_TABLE -- pass list of amounts
                            .
                            .
                            .)

s_chk_amnt              NUMBER;

invoice_list SIMPLEARRAYTYPE;
amount_list NUMBER_TABLE;

BEGIN
      -- check if amount list is null or contains zeros
    IF p_amount_list IS NOT NULL AND p_amount_list.COUNT <> 0 THEN
      FOR r IN p_amount_list.FIRST..p_amount_list.LAST
      LOOP
        s_chk_amnt := s_chk_amnt + p_amount_list(r);
      END LOOP;
    END IF;

Can I declare a list of characters and list of numbers as function input parameters?
I have found some examples with FOREACH element but I don't know how to grab a certain element from number list like in Oracle with p_amount_list(r).

回答1:

CREATE OR REPLACE FUNCTION CREATE_PAYMENT(p_amount_list numeric[])
  RETURNS numeric AS
$func$
DECLARE
   s_chk_amnt numeric := 0; -- init variable!
   r          numeric;
BEGIN
-- IF p_amount_list <> '{}' THEN  -- just noise
   FOREACH r IN ARRAY p_amount_list
   LOOP
      s_chk_amnt := s_chk_amnt + r;
   END LOOP;
-- END IF;

RETURN s_chk_amnt;
END
$func$ LANGUAGE plpgsql

Major points

Oracle's number is numeric in Postgres. But if you don't have fractional digits, you'd rather use int or bigint in Postgres. About type mapping between Oracle and Postgres.
Postgres does not have "table types" like Oracle. Use array types, an array of numeric in this case: numeric[].
The expression IF p_amount_list <> '{}' ... would rule out NULL and "empty array" alike. No need for a second check like in your original. But the IF is not needed at all. For NULL or empty array, the loop isn't entered anyway.
r holds the element itself, not an index to it. (Therefore it must be a matching data type.)

This goes to demonstrate basic syntax of a FOREACH loop in a plpgsql function. Otherwise it would be expensive nonsense, better replaced with a much simpler and faster:

SELECT sum(elem) AS sum_amount
FROM   unnest(p_amount_list) elem;

来源：https://stackoverflow.com/questions/27708234/pl-pgsql-control-structures-for-lists-arrays

标签

postgresql

for-loop

arraylist

plpgsql

control-structure