mysql case语句中断

我使用下面的

case

语句来处理sql中的枚举。但它返回了错误的结果

SELECT  material_name,material_id,grade_id,subject_id,course_term_id,
        CASE grade_id
                WHEN grade_id =  1 THEN "一年级"
                WHEN grade_id =  2 THEN "二年级"
                WHEN grade_id =  3 THEN "三年级"
                WHEN grade_id =  4 THEN "四年级"
                WHEN grade_id =  5 THEN "五年级"
                WHEN grade_id =  6 THEN "六年级"
                WHEN grade_id =  7 THEN "初一"
                WHEN grade_id =  8 THEN "初二"
                WHEN grade_id =  9 THEN "初三"
                WHEN grade_id = 10 THEN "高一"
                WHEN grade_id = 11 THEN "高二"
                WHEN grade_id = 12 THEN "高三"
                ELSE "" END as grade,
        CASE subject_id
                WHEN subject_id =  1 THEN "数学"
                WHEN subject_id =  2 THEN "物理"
                WHEN subject_id =  3 THEN "化学"
                WHEN subject_id =  4 THEN "语文"
                WHEN subject_id =  5 THEN "英语"
                WHEN subject_id =  6 THEN "科学"
                WHEN subject_id =  7 THEN "音乐"
                WHEN subject_id =  8 THEN "绘画"
                WHEN subject_id =  9 THEN "政治"
                WHEN subject_id = 10 THEN "历史"
                WHEN subject_id = 11 THEN "地理"
                WHEN subject_id = 12 THEN "生物"
                WHEN subject_id = 13 THEN "奥数"
                ELSE "" END as subject,
        CASE course_term_id
                WHEN course_term_id = 1 THEN "春"
                WHEN course_term_id = 2 THEN "暑"
                WHEN course_term_id = 3 THEN "秋"
                WHEN course_term_id = 4 THEN "寒"
                ELSE "" END as season,
        created_at, updated_at from sc_materials where material_id in (2025,317,2050);

和输出，其中红色标记的圆圈应带有值而不是空字符串。

当我使用as comment use

ELSE COALESCE（grade_id.））END

时，它显示

这是我在这些字段中使用的数据类型

grade_id    int
subject_id  int 
course_term_id  tinyint

---

好吧，我在你的箱子里发现了一些东西。很抱歉，一开始我没有注意到这一点

案例有两种形式：

CASE <expr1> WHEN <expr2> THEN <result> ...

CASE WHEN <expr3> THEN <result> ...

对于其他CASE表达式也是如此

---

但我也同意@tadman的评论——你应该只使用三个查找表

我建议您通过使用

ELSE COALESCE（grade_id，”）END

和类似的其他case表达式进行调试。您想知道其他案例的价值是多少。@BillKarwin谢谢您的建议，我将结果添加到我的问题中。这需要一个简单的查找表，您可以

加入
。当1时，它不应该是
案例主题\u id…
？
CASE <expr1> WHEN <expr2> THEN <result> ...

CASE WHEN <expr3> THEN <result> ...

    CASE grade_id
            WHEN  1 THEN "一年级"
            WHEN  2 THEN "二年级"
            WHEN  3 THEN "三年级"
            WHEN  4 THEN "四年级"
            WHEN  5 THEN "五年级"
            WHEN  6 THEN "六年级"
            WHEN  7 THEN "初一"
            WHEN  8 THEN "初二"
            WHEN  9 THEN "初三"
            WHEN 10 THEN "高一"
            WHEN 11 THEN "高二"
            WHEN 12 THEN "高三"
            ELSE "" END as grade,