如何从mysql表中获取Last和Secondlast记录

Question

从上面的图片中我有 n 的记录数 cat_id 和 sub_cat_id ，但在图片中只有两个记录。

所以我希望将最后和 secondlast score_in_per值命名为lastScore和latetsScore ..

我该如何检索..？

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

我是这个复杂的mysql逻辑的新手。这就是我试过的..

示例： 假设一个用户电子邮件inststudent@yopmail.com采用相同的测试2次，测试与一个类别和子类别相关联。 所以用户将多次参加测试......

  

从那些记录我想得到最后两个记录的百分比。

Answer 1

如果我理解正确的话;您想要选择特定学生所进行的特定类型考试的两个最新结果。

您没有正确使用LIMIT子句。这是正确的语法：LIMIT {[offset,] row_count | row_count OFFSET offset}。另外，你完全忽略了where子句。

所以查询应该是：

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;

如果一个学生每天可以多次参加考试（如你的形象所示），那么你也应该通过id订购（假设id对于较新的结果总是更大）或更好，只有id：

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

解决此问题的方法之一是使用分区依据 Step1：我按照分区的顺序按日期降序排列了不同cat_id和sub_cat_id的数据。
Step2：我使用了rank1这是最新的得分，并将其与rank2合并，这是第二个最后得分

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;  

如有任何疑问，请与我们联系。

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