How to use SUM when foreign key and primary key matched in MYSQL

Question

Currently I have 2 tables which is document and item table.

CREATE TABLE IF NOT EXISTS `document` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `dateDoc` datetime NOT NULL,
  `numDoc` varchar(45) NOT NULL,
  `idCategory` int(11) DEFAULT NULL,
  `subject` varchar(200) DEFAULT NULL,
  `status` varchar(1) NOT NULL DEFAULT 'A',
  PRIMARY KEY (`id`)
) ENGINE=InnoDB  DEFAULT CHARSET=latin1 AUTO_INCREMENT=155 ;

CREATE TABLE IF NOT EXISTS `item` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `idDoc` int(11) NOT NULL,
  `numItem` int(11) NOT NULL,
  `amount` decimal(14,4) NOT NULL,
  `idTax` varchar(30) DEFAULT NULL,
  `rateTax` decimal(5,2) DEFAULT NULL,
  `amtTax` decimal(12,4) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB  DEFAULT CHARSET=latin1 AUTO_INCREMENT=244 ;

How to sum up the amount and amtTax in Table 'item' if document(id) = item (idDoc).

For example :

(document table)

Document id = 1;

(item table)

id = 1;
idDoc = 1;
amount = 50.00;
amtTax = 10.00;


id = 2;
idDoc = 1;
amount = 30.00;
amtTax = 6.60;

I suppose to get RM96.60.

How to sum up the amount and amtTax in mysql as a new column named (Total) if idDoc match with document table's id? Thank you for your help!

Answer 1

If you want to select all documents with their sums of amounts and amt taxes, use a join with group by over the documents:

SELECT SUM(item.amount) + SUM(item.amtTax) AS Total
FROM document
LEFT JOIN item
    ON document.id = item.idDoc

If you want to select just a single document (eg the one with id 1), you don't need to use group by, just add where clause:

SELECT document.*, sum(item.amount) + sum(item.amtTax) as Total
FROM document LEFT JOIN item ON document.id = item.idDoc
WHERE document.id = 1