Question

I have a table that looks like this

CREATE TABLE `purchases` (
    `id` INT(10) NOT NULL AUTO_INCREMENT,
    `totalAmount` INT(10) NOT NULL DEFAULT '0',
    `purchaseDate` DATETIME NOT NULL,
    PRIMARY KEY (`id`)
)

and another table that stores all the details of the purchases (eg.line items)

CREATE TABLE `purchase_items` (
    `id` INT(10) NOT NULL AUTO_INCREMENT,
    `purchaseId` INT(10) NOT NULL,
    `itemId` INT(10) NOT NULL DEFAULT '0',
    PRIMARY KEY (`id`),
    FOREIGN KEY (`purchaseId`) REFERENCES purchases(id)
)

I get the total purchases on any given day this way

SELECT DATE_FORMAT(purchaseDate, '%m-%d-%Y') AS date,
COUNT(id) AS totalPurchases
FROM purchases
GROUP BY DATE(purchaseDate)

This gives me a result as such

date        totalPurchases
11-18-2010  5
11-19-2010  10
11-20-2010  10

How will I perform a query such that it returns me something like this

date        totalPurchases  totalItems
11-18-2010  5               20
11-19-2010  10              30
11-20-2010  10              25

So I will still be grouping by date but I need to perform a join on ‘purchase_items’ and get the total number of item that were linked to the

• 5 Purchases on 11-18-2010
• 10 Purchases on 11-19-2010
• 10 Purchases on 11-20-2010

Answer 1

Use:

  SELECT DATE_FORMAT(p.purchasedate, '%m-%d-%Y'),
         COUNT(p.id) AS totalPurchases,
         COUNT(pi.itemid) AS totalItems
    FROM PURCHASES p
    JOIN PURCHASE_ITEMS pi ON pi.purchaseid = p.id
GROUP BY DATE_FORMAT(p.purchasedate, '%m-%d-%Y')

If it’s possible that there’s no relation to the PURCHASE_ITEMS tables, use:

   SELECT DATE_FORMAT(p.purchasedate, '%m-%d-%Y'),
          COUNT(p.id) AS totalPurchases,
          COUNT(pi.itemid) AS totalItems
     FROM PURCHASES p
LEFT JOIN PURCHASE_ITEMS pi ON pi.purchaseid = p.id
 GROUP BY DATE_FORMAT(p.purchasedate, '%m-%d-%Y')