我該如何優化這個mysql select + multiple joins查詢？

我正在運行此查詢，但它非常緩慢。在最後一個左連接or子句是什麼停滯不前下來，但我想不出另一種方式來構造查詢，以獲得結果我在尋找：我該如何優化這個mysql select + multiple joins查詢？

SELECT *, 
     DATE_FORMAT(tbl1.pub, '%m/%d/%Y') AS pub_a, 
     CONCAT(tbl1.code1, tbl1.code2) AS code_a 
FROM (tbl1 
     INNER JOIN tbl2 ON tbl1.pkid=tbl2.fkid 
     LEFT JOIN tbl3 ON tbl1.pkid=tbl3.fkid) 
LEFT JOIN tbl4 ON tbl1.person=tbl4.code OR tbl3.person=tbl4.code 
WHERE tbl1.subcat != '' 
    AND tbl1.pub < '2014-01-15 13:20:23' 
    AND tbl1.exp > '2014-01-15 13:20:23' 
ORDER BY tbl1.pub DESC 
LIMIT 0, 50

來源

2014-01-15 user3200064

我們真正喜歡的是當你把它全部寫在這樣的一行上。 – Strawberry

我個人喜歡搞清楚'CREATE TABLE'模式和'SHOW INDEXES FROM'。 – bishop

這是一個長期的射門，但嘗試改變

left join tbl4 on tbl1.person = tbl4.code 
    or tbl3.person = tbl4.code

到

left join tbl4 on tbl4.code in (tbl1.person, tbl3.person)

來源

2014-01-15 21:45:36 RedFilter

謝謝，這加快了一點。 – user3200064

不幸的是，在on條款優化or是不容易的。你可以把它分成兩個查詢，加上一個union：

select * 
from ((SELECT *, 
       DATE_FORMAT(tbl1.pub, '%m/%d/%Y') AS pub_a, 
       CONCAT(tbl1.code1, tbl1.code2) AS code_a 
     FROM (tbl1 
       INNER JOIN tbl2 ON tbl1.pkid=tbl2.fkid 
       LEFT JOIN tbl3 ON tbl1.pkid=tbl3.fkid 
      ) 
       LEFT JOIN tbl4 ON tbl3.person=tbl4.code 
     WHERE tbl1.subcat != '' 
      AND tbl1.pub < '2014-01-15 13:20:23' 
      AND tbl1.exp > '2014-01-15 13:20:23' 
     ORDER BY tbl1.pub DESC 
     LIMIT 0, 50 
     ) union 
     (SELECT *, 
       DATE_FORMAT(tbl1.pub, '%m/%d/%Y') AS pub_a, 
       CONCAT(tbl1.code1, tbl1.code2) AS code_a 
     FROM (tbl1 
       INNER JOIN tbl2 ON tbl1.pkid=tbl2.fkid 
       LEFT JOIN tbl3 ON tbl1.pkid=tbl3.fkid 
      ) 
       LEFT JOIN tbl4 ON tbl1.person=tbl4.code 
     WHERE tbl1.subcat != '' 
      AND tbl1.pub < '2014-01-15 13:20:23' 
      AND tbl1.exp > '2014-01-15 13:20:23' 
     ORDER BY tbl1.pub DESC 
     LIMIT 0, 50 
     ) 
    ) t 
order by pub desc 
limit 0, 50

來源

2014-01-15 22:02:08

我該如何優化這個mysql select + multiple joins查詢？

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