MYSQL how to choose one of unit price - mysql

Question

i have 3 tables
CREATE TABLE IF NOT EXISTS `items` (
`name` varchar(255) COLLATE utf8_unicode_ci NOT NULL,
`category` varchar(255) COLLATE utf8_unicode_ci NOT NULL,
`supplier_id` int(11) DEFAULT NULL,
`item_number` varchar(255) COLLATE utf8_unicode_ci DEFAULT NULL,
`product_id` varchar(255) COLLATE utf8_unicode_ci DEFAULT NULL,
`description` varchar(255) COLLATE utf8_unicode_ci NOT NULL,
`size` varchar(255) COLLATE utf8_unicode_ci NOT NULL DEFAULT '',
`tax_included` int(1) NOT NULL DEFAULT '0',
`cost_price` decimal(23,10) NOT NULL,
`unit_price` decimal(23,10) NOT NULL,
`promo_price` decimal(23,10) DEFAULT NULL,
`start_date` date DEFAULT NULL,
`end_date` date DEFAULT NULL,
`reorder_level` decimal(23,10) DEFAULT NULL,
`item_id` int(10) NOT NULL,
`allow_alt_description` tinyint(1) NOT NULL,
`is_serialized` tinyint(1) NOT NULL,
`image_id` int(10) DEFAULT NULL,
`override_default_tax` int(1) NOT NULL DEFAULT '0',
`is_service` int(1) NOT NULL DEFAULT '0',
`deleted` int(1) NOT NULL DEFAULT '0',
`items_batang_6` tinyint(1) NOT NULL,
`items_batang_55` tinyint(1) NOT NULL,
`items_batang_3` tinyint(1) NOT NULL
) ENGINE=InnoDB AUTO_INCREMENT=255 DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci;
INSERT INTO `items` (`name`, `category`, `supplier_id`, `item_number`, `product_id`, `description`, `size`, `tax_included`, `cost_price`, `unit_price`, `promo_price`, `start_date`, `end_date`, `reorder_level`, `item_id`, `allow_alt_description`, `is_serialized`, `image_id`, `override_default_tax`, `is_service`, `deleted`, `items_batang_6`, `items_batang_55`, `items_batang_3`) VALUES
('PC 60 K', 'Bahan Profil', NULL, '00000000001', 'PC 60 K', '', '', 0, '250.0000000000', '235000.0000000000', NULL, NULL, NULL, NULL, 1, 0, 0, NULL, 0, 0, 0, 0, 0, 0),
('PC 60 DY', 'Bahan Profil', NULL, '00000000002', 'AGK 02B', '', '', 0, '100.0000000000', '50000.0000000000', NULL, NULL, NULL, NULL, 6, 0, 0, NULL, 0, 0, 0, 0, 0, 0)
CREATE TABLE IF NOT EXISTS `price_tiers` (
`id` int(10) NOT NULL,
`name` varchar(255) COLLATE utf8_unicode_ci NOT NULL
) ENGINE=InnoDB AUTO_INCREMENT=35 DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci;
INSERT INTO `price_tiers` (`id`, `name`) VALUES
(1, 'Jendela Kaca Mati Single'),
(2, 'Jendela Kaca Mati Double'),
(3, ' Jendela Swing Single KN KR'),
(4, 'Jendela Swing Double J106')
CREATE TABLE IF NOT EXISTS `items_tier_prices` (
`tier_id` int(10) NOT NULL,
`item_id` int(10) NOT NULL,
`unit_price` decimal(23,10) DEFAULT '0.0000000000',
`percent_off` int(11) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci;
INSERT INTO `items_tier_prices` (`tier_id`, `item_id`, `unit_price`, `percent_off`) VALUES
(1, 1, '200000.0000000000', NULL),
(4, 6, '40000.0000000000', NULL);
What I am trying to accomplish is to display ALL list of items which is connected to price_tiers.name='Jendela Swing Double J106'.
If it doesn't have items_tier_prices.unit_price, column price
will display items.unit_price, but if it has items_tier_prices.unit_price, query will display items_tier_prices.unit_price. so the default to be displayed is items.unit_price. i want to be like this when i have data item_id 6 on items_tier_prices:
item_id price
==============================
1 235000
6 40000
but when i delete data item_id 6 on items_tier_prices:
item_id price
==============================
1 235000
6 50000
what i have tried is:
SELECT items.item_id, if(items_tier_prices.unit_price is null,items.unit_price, items_tier_prices.unit_price ) as unit_price FROM `items`
LEFT JOIN `items_tier_prices`
ON `items_tier_prices`.`item_id`=`items`.`item_id`
LEFT JOIN `price_tiers`
ON `price_tiers`.`id`=`items_tier_prices`.`tier_id`
WHERE `items`.`deleted` = 0
and price_tiers.name='Jendela Swing Double J106'
but it only display item_id 1 when i dont have data of item_id 6 in item_tier_prices
pls help.. many thanks

Answer 1

Currently your join before the WHERE provides (some fields added to explore):
SELECT items.item_id, if(items_tier_prices.unit_price is null,items.unit_price, items_tier_prices.unit_price ) as unit_price,
price_tiers.name,
`items`.`deleted`
FROM `items`
LEFT JOIN `items_tier_prices`
ON `items_tier_prices`.`item_id`=`items`.`item_id`
LEFT JOIN `price_tiers`
ON `price_tiers`.`id`=`items_tier_prices`.`tier_id`
Return
----------
'1', '200000.0000000000', 'Jendela Kaca Mati Single', '0'
'6', '40000.0000000000', 'Jendela Swing Double J106', '0'
Putting the where it returns:
'6', '40000.0000000000'
I do not understand where is the issue, you do not have 2 records on Jendela Swing Double J106.
Regards

Answer 2

Here's what I think you are trying to achieve:
You have items in a table which have a price per unit (unit_price).
IFF (if and only if) there is a relation between a tier and an item, the special price per unit is supposed to show up.
If not, use the original item's unit_price.
In your example, you have two items, IDs 1 and 6, and they are both related to some price tier. However, item #1 is tied to tier #1 and item #6 is tied to tier #4.
Since you are specifically searching for special prices only if the are from tier #4, you need to pass that information to the JOIN statement instead of the WHERE statement. That way, it's not filtered out but can be used to display different prices.
SELECT
i.item_id,
IF(pt.name IS NULL, i.unit_price, itp.unit_price) AS unit_price
FROM
items i
LEFT JOIN items_tier_prices itp
ON itp.item_id = i.item_id
LEFT JOIN price_tiers pt
ON pt.id = itp.tier_id
AND pt.name = "Jendela Swing Double J106"
WHERE i.deleted = 0
This will produce the following output:
item_id unit_price
6 40000.0000000000
1 235000.0000000000
where item #6's price is from the tier special and item #1 shows the price from the items table.