如何從mysql表中獲取Last和Secondlast記錄

Question

從上面的圖像中，我有n條帶cat_id和sub_cat_id的記錄，但是在圖像中只有兩條。

所以我想獲取最后一個和倒數 第二個 score_in_per值，分別命名為lastScore和latetsScore ..

我該如何找回..？

SELECT
(SELECT score_in_per FROM tbl_student_skill_score ORDER BY date DESC LIMIT 2,0)  as lastScore,
(SELECT score_in_per FROM tbl_student_skill_score ORDER BY date DESC LIMIT 1)  as latetsScore

我是這個復雜的mysql邏輯的新手。

例如：可以說，一個用戶的電子郵件是inststudent@yopmail.com采取相同的測試2次，測試鏈接了一個類別和子類別。 因此用戶可以多次進行測試...

從該記錄，我想獲得最后兩個記錄的百分比。

Answer 1

如果我正確理解你的話； 您想選擇特定學生參加的特定類型考試的兩個最新結果。

您沒有正確使用LIMIT子句。 這是正確的語法： LIMIT {[offset,] row_count | row_count OFFSET offset} LIMIT {[offset,] row_count | row_count OFFSET offset} 。 另外，您完全省略了where子句。

因此查詢應為：

SELECT
(SELECT score_in_per FROM tbl_student_skill_score
  WHERE user_email = "email of the user you are interested in"
    AND cat_id = categoryOfTestOfInterest
    AND sub_cat_id = subcategoryOfTestOfInterest
  ORDER BY date DESC LIMIT 1, 1
)AS lastScore,
(SELECT score_in_per FROM tbl_student_skill_score
  WHERE user_email = "email of the user you are interested in"
    AND cat_id = categoryOfTestOfInterest
    AND sub_cat_id = subcategoryOfTestOfInterest
  ORDER BY date DESC LIMIT 1
)AS latetsScore;

如果一個學生一天可以參加多次考試（如您的圖像所示），則您還應該按id排序（假設對於新的結果，該id總是更大）或更好，而僅按id排序：

SELECT
(SELECT score_in_per FROM tbl_student_skill_score
  WHERE user_email = "email of the user you are interested in"
    AND cat_id = categoryOfTestOfInterest
    AND sub_cat_id = subcategoryOfTestOfInterest
  ORDER BY id DESC LIMIT 1, 1
)AS lastScore,
(SELECT score_in_per FROM tbl_student_skill_score
  WHERE user_email = "email of the user you are interested in"
    AND cat_id = categoryOfTestOfInterest
    AND sub_cat_id = subcategoryOfTestOfInterest
  ORDER BY id DESC LIMIT 1
)AS latetsScore;

Answer 2

解決此問題的方法之一是使用Partition By 。
步驟1：我已經按日期的降序對不同的cat_id和sub_cat_id的數據進行了划分。
步驟2：我使用了最新得分的rank1，並將其與倒數第二的rank2合並

with chck as
(select
   cat_id,sub_cat_id,score_in_per,date1,
   row_number() over(partition by cat_id,sub_cat_id order by 
   cat_id,sub_cat_id,date1 desc) as row_num
from tbl)

    select a.*,b.second_last_score from
    (select cat_id,sub_cat_id,score_in_per,date1,row_num as last_score from chck where row_num=1) a
    left join
    (select cat_id,sub_cat_id,score_in_per,date1,row_num as second_last_score from chck where row_num=2) b
    on a.cat_id = b.cat_id and a.sub_cat_id = b.sub_cat_id;  

如有任何查詢，請通知我。

Answer 3

SELECT  
(   SELECT score_in_per     FROM   tbl_student_skill_score WHERE cat_id=1 and sub_cat_id=5 ORDER BY date,id DESC LIMIT 1 ) AS latestScore,
(   SELECT score_in_per     FROM   tbl_student_skill_score WHERE cat_id=1 and sub_cat_id=5 ORDER BY date,id DESC LIMIT 1,1  ) AS lastScore