mysql - MySQL 按等级排序，但需要整数

Question

我想按以下顺序订购作为字符串的等级。

K, 1, 2, 4, .... 12

但我不断得到5, 4, 3, ... 12, K, 1

sims_classroom 中的成绩列是 VARCHAR(255)，表格是 latin1；

我已经尝试了书中的每一个演员和技巧。目前，我通过添加 0 来获得以下技巧。我究竟做错了什么？

SELECT 
        (SELECT district_get_name_function(sod.parent_id, sod.id)) AS 'district_name', 
        (SELECT school_get_name_function(so.id)) AS 'school_name',
        st.teacher_username,
        st.teacher_first_name,
        st.teacher_last_name,
        c.name as 'classroom_name',
        c.grade,
        c.id,
        d.name AS 'discipline_name',
        d.id AS 'discipline_id',
        lc.name AS 'program_name',
        lc.id AS 'program_id'
    FROM sims_classroom c
.
.
.

    ORDER BY 
            CASE lower(sort_direction) WHEN 'asc' THEN
                CASE lower(sort_order)
                    WHEN 'grade' THEN 
                                 CASE c.grade 
                                    WHEN 'K' THEN 0
                                    ELSE (c.grade + 0)
                                 END
                    WHEN 'teachername' THEN lower(st.teacher_first_name)
                    ELSE c.name
                END
            END ASC,
            CASE lower(sort_direction) WHEN 'desc' THEN
                CASE lower(sort_order)
                    WHEN 'grade' THEN 
                                 CASE c.grade 
                                    WHEN 'K' THEN 10000
                                    ELSE (c.grade + 0)
                                 END
                    WHEN 'teachername' THEN lower(st.teacher_first_name)
                    ELSE c.name
                END
            END DESC

Answer 1

您可以为成绩创建一个查找表。它将具有 Grade_Name（即“K”、“1”、“2”等）和作为 int 的 Grade_Order。

你会有这样的记录：

Grade_Name    Grade_Order
K             1
1             2
2             3
3             4

等等。

然后，您可以将该查找表添加到您的 JOIN 和 ORDER BY Grade_Order。

Answer 2

我只能让它工作。

WHEN 'grade' THEN 
                             CASE c.grade 
                                 WHEN 'K' THEN '00'
                                 WHEN '9' THEN '09'
                                 WHEN '8' THEN '08'
                                 WHEN '7' THEN '07'
                                 WHEN '6' THEN '06'
                                 WHEN '5' THEN '05'
                                 WHEN '4' THEN '04'
                                 WHEN '3' THEN '03'
                                 WHEN '2' THEN '02'
                                 WHEN '1-2' THEN '01'
                                 WHEN '1' THEN '01'
                                 ELSE c.grade
                             END