MySQL加入問題

Question

我需要一些MySQL SELECT語句的幫助。不幸的是，這種說法無法正常工作。它似乎根據學校名稱的字母順序排列，而不是reading_percent_proficient_and_advanced。我應該如何解決它？

SET @rank=0; 
SELECT @rank:=@rank+1 as rank, 
     sy.formatted_school_name, 
     FLOOR(d.reading_percent_proficient + d.reading_percent_advanced) AS reading_percent_proficient_and_advanced 
FROM d_test_scores AS d, 
     sy_2010_2011_school_type AS sy 
WHERE sy.school_id = d.school_id 
     AND sy.school_group = 'public school' 
     AND sy.school_type ='elementary' 
ORDER BY reading_percent_proficient_and_advanced DESC 

如果我拿出的加入，那麼這種說法給了我正確的排名（但我沒有那麼學校名稱）：

SET @rank=0; 
SELECT @rank:=@rank+1 as rank, 
     d.school_id, 
     FLOOR(d.reading_percent_proficient + d.reading_percent_advanced) AS reading_percent_proficient_and_advanced 
FROM d_test_scores AS d 
ORDER BY reading_percent_proficient_and_advanced DESC; 

什麼是我加入的問題？

Answer 1

（猜測）我相信排序是在執行ORDER BY排序之前計算的。在原始查詢中，只是在ORDER BY之前以您想要的順序返回結果，因此排名正確，但在高級查詢中，結果最初會以不同的順序返回。

嘗試將排名添加到已經訂購設置（子查詢）的學校名稱和能力評級。

Answer 2

實際上我沒有看到任何JOIN關鍵字，試試這可能嗎？

SET @rank=0; 
SELECT @rank:=@rank+1 as rank, 
     sy.formatted_school_name, 
     FLOOR(d.reading_percent_proficient + d.reading_percent_advanced) AS reading_percent_proficient_and_advanced 
FROM d_test_scores d JOIN sy_2010_2011_school_type sy on sy.school_id = d.school_id 
WHERE sy.school_group = 'public school' 
     AND sy.school_type ='elementary' 
ORDER BY reading_percent_proficient_and_advanced DESC 

只是一個猜測。