How to loop through results in an sproc? - mysql

Question

I'm learning about stored procedures in mysql (5.5), and have hit a bit of a mental block here about what can be done using sprocs.
The base data looks like this:
select * from fruit;
name | variety | price | quantity
---------------------------------
Pear Comice - 15 - 2
Pear Barlett - 20 - 3
Pear Anjou - 20 - 3
Apple Red - 10 - 7
etc
How do I get the combined monetary value of ALL types of a fruit, say, all Pear types?
I got as far as making this sproc which will get the value of a single variety of a fruit.
DROP PROCEDURE IF EXISTS getStockValue;
DELIMITER // CREATE PROCEDURE `getStockValue`(
IN variety varchar(20),
IN vat BOOLEAN,
OUT tot DECIMAL(8,2)
)
BEGIN
DECLARE nett_value INT;
SELECT (quantity*price) INTO nett_value from fruit where variety = variety;
IF vat = 1 THEN
SELECT (nett_value*20/100)+(nett_value) INTO tot;
ELSE
SELECT nett_value INTO tot;
END IF;
SELECT tot;
END;// DELIMITER ;
CALL getStockValue('Comice',1,#tot);
So from my base data you see that without VAT it should come back with the total 150, and with VAT 180.
Do I have another sproc which loops through a result set somehow?
What is the best way to tackle this so that this computation stays on the database server?
Is this where a cursor would be used?
I've read an awful lot about when to/not to use sprocs, but I have an interview with a company that have warned me they rely heavily on them already.
EDIT - in order to clarify my overall question.
How do I get from where I am:
CALL getStockValue('Comice',1,#tot);
// gives 36
(in hindsight should be renamed getStockValueByVariety())
To where I want to be:
CALL getStockValueByName('Pear',1,#tot);
// gives 180 - because it gets ALL Pear types, not just the variety Comice
FINALLY - twigged, I was missing a GROUP BY ...
SELECT SUM(price*quantity) as tot
FROM fruit
WHERE name = 'Pear'
GROUP BY name;

Answer 1

use a CASE statement and just return the value from the stored procedure.
SELECT
CASE vat
WHEN 1 THEN (((quantity*price)*20/100) + (quantity * price))
ELSE (quantity*price)
END AS nett_value
FROM fruit;
If you want the sum total of all of a particular variety, then SUM it
SELECT
SUM(CASE vat
WHEN 1 THEN (((quantity*price)*20/100) + (quantity * price))
ELSE (quantity*price)
END) AS tot
FROM fruit
WHERE variety = #variety
GROUP BY
name