problem with updating table in mysql procedures - mysql

Question

I am creating a procedure that updates any invoice with unpaid status for more than 30 days to 'OVERDUE'. However with my current code whenever I am calling this procedure even the invoice which does not have UNPAID status gets its status updated to OVERDUE.
CREATE procedure sync_invoice()
begin
declare dDate date;
declare stat varchar(20);
declare d_finished int default 0;
declare d_array cursor for
select DATEISSUED, STATUS from invoice;
declare continue handler for not found set d_finished = 1;
open d_array;
repeat
fetch d_array into dDate, stat;
if (datediff(current_date(), dDate)> 30 )then
update invoice
set STATUS = 'OVERDUE'
where stat = 'UNPAID';
end if;
until d_finished
end repeat;
close d_array;
-- code
end
//
here is the invoice table
CREATE TABLE IF NOT EXISTS `invoice` (
`INVOICENO` INT(11) NOT NULL AUTO_INCREMENT,
`CAMPAIGN_NO` INT(11) NOT NULL,
`DATEISSUED` DATE NULL DEFAULT NULL,
`DATEPAID` DATE NULL DEFAULT NULL,
`BALANCEOWING` INT(11) NULL DEFAULT NULL,
`STATUS` VARCHAR(20) NULL DEFAULT NULL,
PRIMARY KEY (`INVOICENO`, `CAMPAIGN_NO`),
INDEX `FK_INVOICE_SENDS2_CAMPAIGN_idx` (`CAMPAIGN_NO` ASC),
CONSTRAINT `FK_INVOICE_SENDS2_CAMPAIGN`
FOREIGN KEY (`CAMPAIGN_NO`)
REFERENCES `campaign` (`CAMPAIGN_NO`)
ON DELETE RESTRICT
ON UPDATE RESTRICT)
AUTO_INCREMENT = 6;

Answer 1

Ok so there are a few wrong things here:
CREATE procedure sync_invoice()
begin
declare dDate date;
declare stat varchar(20);
declare d_finished int default 0;
declare d_array cursor for
select DATEISSUED, STATUS from invoice;
declare continue handler for not found set d_finished = 1;
open d_array;
repeat
-- The loop will be executed for each entry into invoice
fetch d_array into dDate, stat;
-- For each, if it's old enough, regardless of the status...
if (datediff(current_date(), dDate)> 30 )then
-- This SQL request, which is called over the whole invoice table is executed
update invoice
set STATUS = 'OVERDUE' -- Effectively setting the status to overdue
where stat = 'UNPAID'; -- for each entry, so far that the one inspected is UNPAID
end if;
until d_finished
end repeat;
close d_array;
-- code
end
So basically, with this code, you'll always set every invoice to OVERDUE so long that there is a single, 30+ days old UNPAID invoice in the table.
Some way around this include replacing the whole content of the procedure by the single appropriate UPDATE call:
Update invoice Set STATUS = 'OVERDUE' Where datediff(current_date(), DATEISSUED) > 30 And STATUS = 'UNPAID';
Edit: To clarify, you could 'fix' the whole thing by replacing 'stat' at line where stat = 'UNPAID'; by 'STATUS', but you would still be executing way too many instructions without any reason to, effectively iterating through your whole invoice table as many time as you have 30+ days old invoices.
But in practice, SQL is a quite powerful language in which you might not need to loop yourself for tasks working with a single entry in a table. Statements such as UPDATE ... WHERE ... do it for you. c:
Loops and cursor, then, become useful when you have to do process that need to consider multiple entry at once.