MySQL的多次join曹景偉至尊放緩

Question

我試圖讓它們不我們的網站中使用的所有圖像的出口（到表）。我的工作代碼在小數據集上表現良好，但仍然尚未從我們的超過4,000張圖像的數據集返回結果。我有類似的代碼下面我select語句：

SELECT a.id, a.image_name, a.last_modified, c1.val 
    FROM a 
    /*file name could be used in table 'r' in the image1, image2, or image3 fields*/ 
    LEFT JOIN r ON a.image_name = r.image1 
     OR a.image_name = r.image2 
     OR a.image_name = r.image3 
    /*file name could be used anywhere within c.val field*/ 
    LEFT JOIN c c1 ON c1.val LIKE CONCAT('%', a.image_name,'%') 
    /*get the page_id where the image name is found in c*/ 
    LEFT JOIN p p1 ON p1.page_id = c1.page_id 
    WHERE a.type = 'Image' /*only images on this query*/ 
    AND r.image1 IS NULL /*no references in r.image1*/ 
    AND r.image2 IS NULL /*no references in r.image2*/ 
    AND r.image3 IS NULL /*no references in r.image3*/ 
    AND c1.val IS NULL /*no references in c.val OR...*/ 
    /*in the page where it was found, see if the page is a deleted page*/ 
    OR a.id NOT IN (SELECT a.id FROM a 
     LEFT JOIN c c2 ON c2.val LIKE CONCAT('%', a.image_name, '%') 
     LEFT JOIN p p2 ON p2.page_id = c2.page_id 
     WHERE p2.deleted IS NULL) /*deleted IS NULL means the page is not deleted*/ 
    ORDER BY a.last_modified DESC 

實際上有兩種情況時，圖像會在這個出口顯示：

1. 它沒有發現任何地方
2. 它的發現一個已被刪除的頁面

第一個是由外部SELECT減去OR a.id NOT IN...部分得到的。第二個是使用內部SELECT獲得的，我確保id不包含在未刪除的頁面中。

我試過將OR a.id NOT IN...更改爲OR p1.deleted IS NOT NULL以取出內部SELECT的開銷，但是這給了我在刪除的頁面中找到的所有圖像，而不一定是僅在刪除的頁面中找到的圖像。

我已經試過索引p.deleted，r.image1，r.image2和r.image3與效率沒有增加字段。我也試着讓BLOB字段，c.val，FULLTEXT索引，這也沒有幫助。

a.id，a.image_name，c.page_id和p.page_id已經索引。

再次，這是工作的代碼，但我只是想提高性能，所以我們可以把代碼投入生產使用我們全面的數據集。感謝您提前回復。

Answer 1

對不起雁追我的意見開始，我應該看着查詢接近;但這可能會有所幫助......

SELECT a.id, a.image_name, a.last_modified, c1.val 
FROM a 
LEFT JOIN (
    /*file name could be used in table 'r' in the image1, image2, or image3 fields*/ 
    SELECT 1 AS matched, image1 AS image FROM r 
    UNION SELECT 1, image2 FROM r 
    UNION SELECT 1, image3 FROM r 
) AS r2 ON a.image_name = r2.image 
/*file name could be used anywhere within c.val field*/ 
LEFT JOIN c c1 ON c1.val LIKE CONCAT('%', a.image_name,'%') 
/*get the page_id where the image name is found in c*/ 
LEFT JOIN p p1 ON p1.page_id = c1.page_id 
WHERE a.type = 'Image' /*only images on this query*/ 
AND r2.matched IS NULL /*no references in r.image1, r.image2, or r.image3*/ 
AND (
    c1.val IS NULL /*no references in c.val OR...*/ 
    /*in the page where it was found, see if the page is a deleted page*/ 
    OR a.id NOT IN (
     SELECT a.id 
     FROM a 
      LEFT JOIN c c2 ON c2.val LIKE CONCAT('%', a.image_name, '%') 
      LEFT JOIN p p2 ON p2.page_id = c2.page_id 
     WHERE p2.deleted IS NULL 
    ) /*deleted IS NULL means the page is not deleted*/ 
) 
ORDER BY a.last_modified DESC