MySQL的內部連接語句錯誤

Question

我收到以下錯誤：當我運行以下

1052 - Column 'product_id' in field list is ambiguous

：

SELECT `product_id`, `product_name` 
FROM `products` 
INNER JOIN `products_has_product_category` 
    ON `products.product_id` = `products_has_product_category.product_id` 
    AND `products_has_product_category.category_id` = 1 
ORDER BY `products.product_name` 

我PRODUCTS表已經

product_id, product_name, etc 

我products_has_product_category表有

product_id, category_id 

這是我第一次嘗試加入，所以我很感謝幫助！

Answer 1

您需要指定product_id來自哪個表。由於product_id在兩個表格中，所以當您需要指定要從哪個表格中獲取值時，您需要使用SELECT。隨着表的別名：

SELECT p.product_id, p.product_name 
FROM `products` p 
INNER JOIN `products_has_product_category` pc 
    ON p.product_id = pc.product_id 
    AND pc.category_id = 1 
ORDER BY p.product_name 

無表的別名：

SELECT `products`.`product_id`, `products`.`product_name` 
FROM `products` 
INNER JOIN `products_has_product_category` 
    ON `products.product_id` = `products_has_product_category.product_id` 
    AND `products_has_product_category.category_id` = 1 
ORDER BY `products.product_name` 

Answer 2

如果我正確理解你的意圖，你可能是指在哪裏，而不是AND：

SELECT `products`.`product_id`, `products`.`product_name` 
      FROM `products` 
      INNER JOIN `products_has_product_category` 
      ON `products.product_id` = `products_has_product_category.product_id` 
      WHERE `products_has_product_category.category_id` = 1 
      ORDER BY `products.product_name`