我需要參加嗎？

Question

我有3個表：產品，products_description，products_to_categories

這是我的sql：

SELECT `products`.`products_model`, 
       `products_description`.`products_name` 
FROM   products, 
       products_description, 
       products_to_categories 
WHERE  `products`.`products_id` = `products_description`.`products_id` = 
                                         `products_to_categories`. `products_id` 
       AND `products_to_categories`.`categories_id` <> '91' 
ORDER  BY `products`.`products_model` DESC 

所有這三個表都將products_id作為主鍵，我正在嘗試基於此鏈接所有這三個表。 我認為我需要加入，因為我似乎無法使所有三個在一個陳述中都相等？

Answer 1

你可以用JOIN來做，但是如果你想使用Where語句那么好，但是你必須使用AND來實現它

SELECT `products`.`products_model`, `products_description`.`products_name`
FROM products, products_description, products_to_categories
WHERE `products`.`products_id` =  `products_description`.`products_id` 
   AND `products`.`products_id`= `products_to_categories`.`products_id` 
   AND `products_to_categories`.`categories_id` <> '91' 
ORDER BY `products`.`products_model` DESC

Answer 2

select p.`products_model`,
    pd.`products_name`
from products p
inner join products_description pd on p.`products_id` = pd.`products_id`
inner join products_to_categories pc on p.`products_id` = pc.`products_id`
where pc.`categories_id` <> '91'
order by p.`products_model` desc

Answer 3

嘗試

SELECT products_model, products_name
  FROM products
       NATURAL JOIN products_description
       NATURAL JOIN products_to_categories;

Answer 4

無論如何，更現代的JOIN通常優先於舊的隱式連接語法。 它提供了有關表如何關聯的更易讀的圖片，並且通過僅在WHERE包括實際的限制條件而允許使用更清晰的WHERE子句。

SELECT 
  `products`.`products_model`,
  `products_description`.`products_name`
FROM 
  products
  JOIN products_description ON products.product_id = products_description.product_id
  JOIN products_to_categories ON products.product_id = products_to_categories.product_id
WHERE  `products_to_categories`.`categories_id` <> '91' 
ORDER BY `products`.`products_model` DESC

Answer 5

盡量不要在FROM子句中使用逗號。 它是sql標准的更舊版本的延續，並不再被認為是一個好習慣。 幾乎在任何地方你使用TableA,TableB語法，你現在應該學習使用TableA INNER JOIN TableB ON 。

但是，在這種情況下，你可以像這樣逃避它：

SELECT `products`.`products_model`, `products_description`.`products_name`
FROM products, products_description, products_to_categories
WHERE `products`.`products_id` =  `products_description`.`products_id` 
    AND `products`.`products_id` = `products_to_categories`. `products_id` 
    AND `products_to_categories`.`categories_id` <> '91' 
ORDER BY `products`.`products_model` DESC

但是，你真的應該學會這樣寫：

SELECT `products`.`products_model`, `products_description`.`products_name`
FROM products
INNER JOIN products_description ON products.products_id = `products_description`.`products_id`
INNER JOIN `products_to_categories` ON `products_to_categories`.`products_id` = `products`.`products_id`
WHERE `products_to_categories`.`categories_id` <> '91' 
ORDER BY `products`.`products_model` DESC

Answer 6

    SELECT `products`.`products_model`, `products_description`.`products_name`

FROM產品，products_description，products_to_categories products 。 products_id = products_description 。 products_id AND products_to_categories 。 products_id = products 。 products_id AND products_description 。 products_id = products_to_categories 。 products_id products_to_categories 。 products_id AND products_to_categories 。 categories_id <>'91'ORDER BY products 。 products_model DESC

試試這個，我認為它像您的查詢一樣更好