Converting SQL Select Query to PL/SQL Anonymous Block (ORACLE) - oracle

Question

I have written a standard SQL Select Query to select the zip code in which the largest number of sales were. I now need to convert it to an anonymous PL/SQL block, however I'm still very "green" with PL/SQL and really don't have much of an idea as to how to accomplish this. Also, I need to incorporate a LIMIT into the PL/SQL anonymous block that will only display the lowest numeric zip code in the event of a tie.
Here are the tables w/some data:
CREATE TABLE CUSTOMERS
(customerID INT PRIMARY KEY,
customerZip VARCHAR(15) NOT NULL);
CREATE TABLE SALES
(saleID INT PRIMARY KEY,
customerID INT,
CONSTRAINT SALES_FK1 FOREIGN KEY (customerID) REFERENCES CUSTOMERS(customerID));
INSERT INTO CUSTOMERS (customerID, customerZIP) VALUES (1, '20636');
INSERT INTO CUSTOMERS (customerID, customerZIP) VALUES (2, '20619');
INSERT INTO CUSTOMERS (customerID, customerZIP) VALUES (3, '20670');
INSERT INTO CUSTOMERS (customerID, customerZIP) VALUES (4, '20670');
INSERT INTO CUSTOMERS (customerID, customerZIP) VALUES (5, '20636');
INSERT INTO SALES (saleID, customerID) VALUES (1, 1);
INSERT INTO SALES (saleID, customerID) VALUES (2, 2);
INSERT INTO SALES (saleID, customerID) VALUES (3, 3);
INSERT INTO SALES (saleID, customerID) VALUES (4, 4);
INSERT INTO SALES (saleID, customerID) VALUES (5, 5);
And here's the SQL query I wrote:
SELECT C.customerZip, COUNT (*) AS "MOST_SALES_byZIP"
FROM SALES S
INNER JOIN CUSTOMERS C
ON S.customerID = C.customerID
GROUP BY C.customerZip
HAVING COUNT (*) >= ALL
(SELECT COUNT(*)
FROM SALES S
INNER JOIN CUSTOMERS C
ON S.customerID = C.customerID
GROUP BY C.customerZip)
ORDER BY C.customerZip;
Basically, I first need to know how to "convert" this into a PL/SQL anonymous block. Then, I need to know how I can limit the results to only show the lowest numeric zip code if there is a tie between two or more.
I have an SQL fiddle Schema built here, if it helps: http://sqlfiddle.com/#!4/ca18bf/2
Thank you!

Answer 1

80% of good PL/SQL programming is good SQL coding.
In your problem: first, in SQL, to select the lowest numeric zip code from among those tied for most sales, you can do a join followed by aggregation by zip code, as you did already - and then use the aggregate LAST function. Like so:
select min(customerzip) keep (dense_rank last order by count(*)) as selected_zip
from sales inner join customers using (customerid)
group by customerzip
;
SELECTED_ZIP
---------------
20636
Now it is easy to use this in an anonymous block (if you have to - for whatever reason). SET SERVEROUTPUT ON is not part of the PL/SQL code; it is a command to the interface program, to instruct it to display the content of the output buffer on screen.
set serveroutput on
declare
selected_zip integer;
begin
select min(customerzip) keep (dense_rank last order by count(*))
INTO selected_zip -- this is the PL/SQL part!
from sales inner join customers using (customerid)
group by customerzip
;
dbms_output.put_line('Selected zip is: ' || selected_zip);
end;
/
PL/SQL procedure successfully completed.
Selected zip is: 20636

Answer 2

Here's an option. Create a function since an anonymous block can only print to STDOUT, it can't return something into a variable
The having clause is remove and simply order by count,zip so that top count wins then top count + top zip based on the order. Added in fetch first 1 rows ONLY to only get the 1 row then returned it from the function.
SQL> CREATE OR REPLACE FUNCTION getlowest RETURN NUMBER AS
l_ret NUMBER;
BEGIN
FOR r IN (
SELECT
c.customerzip,
COUNT(*) AS "MOST_SALES_byZIP"
FROM
sales s
INNER JOIN customers c ON s.customerid = c.customerid
GROUP BY
c.customerzip
order by
COUNT(*), c.customerzip
fetch first 1 rows ONLY
) LOOP
l_ret := r.customerzip;
END LOOP;
RETURN l_ret;
END;
/
SQL> show errors;
SQL>
SQL> select getlowest from dual
2 /
20619
SQL>

Answer 3

If the aim is to return a result set, then the PL/SQL block to do that would be
-- [Declare the host ref cursor according to the calling tool/language]
-- e.g. in SQL*Plus
var resultset refcursor
begin
open :resultset for
select c.customerzip, count(*) as most_sales_byzip
from sales s
join customers c on s.customerid = c.customerid
group by c.customerzip
having count(*) >= all
( select count(*) from sales s
join customers c on s.customerid = c.customerid
group by c.customerzip )
order by c.customerzip;
end;
From Oracle 12.1 onwards you can use implicit result sets:
declare
rc sys_refcursor;
begin
open rc for
open :resultset for
select c.customerzip, count(*) as most_sales_byzip
from sales s
join customers c on s.customerid = c.customerid
group by c.customerzip
having count(*) >= all
( select count(*) from sales s
join customers c on s.customerid = c.customerid
group by c.customerzip )
order by c.customerzip;
dbms_sql.return_result(rc);
end;
However we already have SQL to do this so it seems a bit pointless.