Mysql的DISTINCT和COUNT查詢

Question

即時通訊有問題獲得一個查詢輸出我怎麼想，

SELECT 
    `orders`.`item_id`, 
    `products`.`item_code`, 
    `products`.`item_name`, 
    `orders`.`quantity` 
FROM 
    `orders` 
    JOIN `products` ON `orders`.`item_id` = `products`.`id` 
    JOIN `suppliers` ON `products`.`supplier_ref` = `suppliers`.`supplier_ref` 
WHERE 
    `suppliers`.`id` = 159 
    AND `orders`.`order_status` = 'NOTED' 

這是返回結果：

item_id item_code item_name   quantity 
1271 RA001G Green Mop Bucket 12L 2 
1270 RA001  Blue Mop Bucket 12L 1 
1270 RA001  Blue Mop Bucket 12L 1 

，但我想它帶回不同的ITEM_ID與數量加在一起如何，當我已經嘗試添加不同並計數我最終只有一行返回。

Answer 1

如果要總結同一商品的數量，請嘗試使用分組 over item_id。就像這樣：

SELECT 
    `orders`.`item_id`, 
    `products`.`item_code`, 
    `products`.`item_name`, 
    sum(`orders`.`quantity`) as quantity, 
FROM 
    `orders` 
    JOIN `products` ON `orders`.`item_id` = `products`.`id` 
    JOIN `suppliers` ON `products`.`supplier_ref` = `suppliers`.`supplier_ref` 
WHERE 
    `suppliers`.`id` = 159 
    AND `orders`.`order_status` = 'NOTED' 
    GROUP BY `orders`.`item_id`, 
     `products`.`item_code`, 
     `products`.`item_name` 

Answer 2

請BY子句

SELECT 
`orders`.`item_id`, 
`products`.`item_code`, 
`products`.`item_name`, 
sum(`orders`.`quantity`) as quantity 
FROM 
    `orders` 
    JOIN `products` ON `orders`.`item_id` = `products`.`id` 
    JOIN `suppliers` ON `products`.`supplier_ref` = `suppliers`.`supplier_ref` 
WHERE 
`suppliers`.`id` = 159 AND `orders`.`order_status` = 'NOTED' 
group by 
`orders`.`item_id`;