MySQL根據多個表條件選擇

Question

我正在測驗網站上工作，需要基於他們剛剛進行的測驗來建議用戶可能會喜歡的測驗。基本上，如果他們剛剛參加的測驗有一個標籤，我需要使用相同的標籤再抽取一次測驗。否則，請從同一類別中抽取另一個測驗。

我的工作方式是按照我希望的方式工作90％，但對我來說這似乎很笨重。不工作的10％是我忘了添加一個條件，它只提取活動的測驗。就像WHERE q.active = 1，但無論我在哪裏或如何添加該條件，它都無法按計劃運行。我要麼獲得一個空集或者在條件被添加之前得到的結果相同。

編輯：

爲了澄清，讀取由@RiggsFolly評論後...

如果我添加AND q.active = 1給我的第一WHERE條款，只有一個其他測驗同一個標籤，它是不活躍我收到一個空集，而不是從類別選擇語句接收結果。將AND q.active = 1僅添加到類別選擇語句，而不是標記選擇語句返回適當的結果，如果沒有使用相同標記的測驗。

SELECT 
    IFNULL(q.meta_title, q.title) AS title, 
    IFNULL(url, title) AS url, 
    1 istag 
FROM tag_index t 
LEFT JOIN tag_index ti 
    ON ti.tag_id = t.tag_id 
LEFT JOIN quizzes q 
    ON q.id = ti.quiz_id 
WHERE t.quiz_id = :quiz_id 
    AND ti.quiz_id != t.quiz_id 

UNION ALL 

SELECT 
    IFNULL(q.meta_title, q.title) AS title, 
    IFNULL(url, title) AS url, 
    0 istag 
FROM category_index c 
LEFT JOIN category_index ci 
    ON ci.category_id = c.category_id 
LEFT JOIN quizzes q 
    ON q.id = ci.quiz_id 
WHERE c.quiz_id = :quiz_id 
    AND ci.quiz_id != c.quiz_id 
    AND NOT EXISTS 
     (SELECT 1 FROM tag_index WHERE quiz_id = :quiz_id) 
ORDER BY RAND() LIMIT 1 

任何幫助或建議將不勝感激！

Answer 1

您還需要添加active = 1條件到您的子查詢：

SELECT 
    IFNULL(q.meta_title, q.title) AS title, 
    IFNULL(url, title) AS url, 
    1 istag 
FROM tag_index t 
LEFT JOIN tag_index ti 
    ON ti.tag_id = t.tag_id 
LEFT JOIN quizzes q 
    ON q.id = ti.quiz_id 
WHERE t.quiz_id = :quiz_id 
    AND ti.quiz_id != t.quiz_id 
    AND q.active = 1 

UNION ALL 

SELECT 
    IFNULL(q.meta_title, q.title) AS title, 
    IFNULL(url, title) AS url, 
    0 istag 
FROM category_index c 
LEFT JOIN category_index ci 
    ON ci.category_id = c.category_id 
LEFT JOIN quizzes q 
    ON q.id = ci.quiz_id 
WHERE c.quiz_id = :quiz_id 
    AND ci.quiz_id != c.quiz_id 
    AND q.active = 1 
    AND NOT EXISTS 
     (SELECT 1 
     FROM tag_index t 
     JOIN tag_index ON ti.tag_id = t.tag_id 
     JOIN quizzes ON q.id = ti.quiz_id 
     WHERE t.quiz_id = :quiz_id 
      AND ti.quiz_id != t.quiz_id 
      AND q.active = 1) 
ORDER BY RAND() LIMIT 1 

但是你不需要那麼再選擇在所有你可以通過istag第一順序：

SELECT 
    IFNULL(q.meta_title, q.title) AS title, 
    IFNULL(url, title) AS url, 
    1 istag 
FROM tag_index t 
LEFT JOIN tag_index ti 
    ON ti.tag_id = t.tag_id 
LEFT JOIN quizzes q 
    ON q.id = ti.quiz_id 
WHERE t.quiz_id = :quiz_id 
    AND ti.quiz_id != t.quiz_id 
    AND q.active = 1 

UNION ALL 

SELECT 
    IFNULL(q.meta_title, q.title) AS title, 
    IFNULL(url, title) AS url, 
    0 istag 
FROM category_index c 
LEFT JOIN category_index ci 
    ON ci.category_id = c.category_id 
LEFT JOIN quizzes q 
    ON q.id = ci.quiz_id 
WHERE c.quiz_id = :quiz_id 
    AND ci.quiz_id != c.quiz_id 
    AND q.active = 1 
ORDER BY istag DESC, RAND() LIMIT 1 

Answer 2

簡易解決方案

在我看來，加載有問題的測驗的tag_id和category_id。然後像你嘗試一樣使用UNION運行一個簡單的查詢。這將簡化很多事情並減少連接數量。

要與大的查詢

SELECT 
    quiz_pool.quiz_id id, 
    IFNULL(q.meta_title, q.title) AS title, 
    IFNULL(q.url, q.title) AS url 
FROM (

    /* IDs of all quizzes with same tag */ 
    SELECT ti.quiz_id, istag = 1 
    FROM tag_index ti 
    WHERE ti.tag_id IN(SELECT tag_id FROM tag_index WHERE quiz_id = :quiz_id) 
     AND ti.quiz_id <> :quiz_id 
    LIMIT 0, :quiz_count 

    UNION ALL 

    /* IDs of all quizzes with same category */ 
    SELECT ci.quiz_id, istag = 0 
    FROM category_index ci 
    WHERE ci.category_id IN(SELECT category_id FROM category_index WHERE quiz_id = :quiz_id) 
     AND ci.quiz_id <> :quiz_id 
    LIMIT 0, :quiz_count 

) quiz_pool 
INNER JOIN quizzes q ON q.id = quiz_pool.quiz_id AND q.active = 1 
ORDER BY quiz_pool.istag DESC, RAND() 
LIMIT 0, :quiz_count 

這裏做這一切，你可以設置：quiz_count，你想取回按你的邏輯測驗的次數。它將首先查找具有相同標籤的測驗，然後從同一類別進行測驗，並將測驗隨機化。

希望它有幫助。