SQL - 組合查詢

Question

我有兩個完全按照我想要的查詢，但是，我想嘗試將它們組合起來。

查詢1：

SELECT DISTINCT categories.id FROM categories 
    INNER JOIN product_categories 
        ON product_categories.category_id=categories.id 
    INNER JOIN products 
        ON product_categories.product_id=products.id 
    WHERE 
        categories.is_sub_cat='1' AND 
        categories.is_paused!='1' AND 
        products.nexus='1'

查詢2：

SELECT DISTINCT categories.top_cat FROM categories 
    INNER JOIN product_categories 
        ON product_categories.category_id=categories.id 
    INNER JOIN products 
        ON product_categories.product_id=products.id 
    WHERE 
        categories.top_cat!='0' AND 
        categories.is_paused!='1' AND 
        products.nexus='1'

是否可以將這些組合成1個查詢，或者我應該在完成兩個查詢之后將結果數組合並到PHP中？

Answer 1

您可以使用UNION合並兩個查詢

SELECT DISTINCT categories.id FROM categories 
    INNER JOIN product_categories 
        ON product_categories.category_id=categories.id 
    INNER JOIN products 
        ON product_categories.product_id=products.id 
    WHERE 
        categories.is_sub_cat='1' AND 
        categories.is_paused!='1' AND 
        products.nexus='1'
UNION 

SELECT DISTINCT categories.top_cat FROM categories 
    INNER JOIN product_categories 
        ON product_categories.category_id=categories.id 
    INNER JOIN products 
        ON product_categories.product_id=products.id 
    WHERE 
        categories.top_cat!='0' AND 
        categories.is_paused!='1' AND 
        products.nexus='1'

Answer 2

你可以用的時候用

SELECT case when (categories.is_sub_cat='1' AND  categories.is_paused!='1' AND 
        products.nexus='1') then categories.id
        else categories.top_cat end  as id
    FROM categories 
    INNER JOIN product_categories 
        ON product_categories.category_id=categories.id 
    INNER JOIN products 
        ON product_categories.product_id=products.id 

Answer 3

您可以將查詢組合為

SELECT DISTINCT categories.id, categories.top_cat FROM categories 
    INNER JOIN product_categories 
        ON product_categories.category_id=categories.id 
    INNER JOIN products 
        ON product_categories.product_id=products.id 
    WHERE 
        ( categories.is_sub_cat='1' OR categories.top_cat!='0' ) AND 
        categories.is_paused!='1' AND 
        products.nexus='1'

或者，如果列categories.id和categories.top_cat具有相同的數據類型，或者能夠轉換為相同的數據類型，則可以使用UNION ALL 。

Answer 4

是的，UNION似乎是一個合法的選擇。 對於你的情況，它應該沒關系，因為你是從同一個表中選擇，但作為旁注，你應該知道，當使用UNION時，你需要在表中具有相同數量的列（即如果它們不同）。

Answer 5

您可以使用WHERE子句中的條件執行此操作：

SELECT DISTINCT c.id
FROM categories c INNER JOIN
     product_categories pc
     ON pc.category_id = c.id INNER JOIN
     products p
     ON pc.product_id = p.id 
WHERE p.nexus = 1 AND
      c.is_paused <> 1 AND
      (c.is_sub_cat = 1 OR
       c.top_cat <> 0 
      );

注意：

• 表別名使查詢更易於編寫和讀取。
• 假設列是數字，請不要將值與字符串進行比較。 盡量避免類型轉換問題。