为用户定义的函数提供无效枚举值时出现令人困惑的错误

我有一个被调用的函数GET_TRANSLATION，它可以根据提供的枚举值基于不同的选择查询返回不同的结果。这是完整的代码：

CREATE FUNCTION GET_TRANSLATION(preferredLanguageId BIGINT, backupLanguageId BIGINT, entityId BIGINT, translationSubject ENUM('CROP_NAME', 'CROP_VARIETY_NAME', 'JOURNAL_TITLE', 'SOIL_TYPE', 'COUNTRY', 'PROVINCE', 'PLACE'))
RETURNS VARCHAR(255) DETERMINISTIC
BEGIN
    CASE
        WHEN translationSubject = 'CROP_NAME' THEN
            RETURN (SELECT COALESCE((SELECT s.translatedName FROM CropNameTranslation s WHERE s.language_id = preferredLanguageId AND s.parent_id = entityId AND s.approved = TRUE LIMIT 1),
            (SELECT s.translatedName FROM CropNameTranslation s WHERE s.language_id = backupLanguageId AND s.parent_id = entityId AND s.approved = TRUE LIMIT 1), (SELECT s.translatedName FROM CropNameTranslation s WHERE s.parent_id = entityId AND s.approved = TRUE LIMIT 1)));
        WHEN translationSubject = 'CROP_VARIETY_NAME' THEN
            RETURN (SELECT COALESCE((SELECT s.translatedName FROM CropVarietyName s WHERE s.language_id = preferredLanguageId AND s.parent_id = entityId AND s.approved = TRUE LIMIT 1),
            (SELECT s.translatedName FROM CropVarietyName s WHERE s.language_id = backupLanguageId AND s.parent_id = entityId AND s.approved = TRUE LIMIT 1), (SELECT s.translatedName FROM CropVarietyName s WHERE s.parent_id = entityId AND s.approved = TRUE LIMIT 1)));
        WHEN translationSubject = 'JOURNAL_TITLE' THEN
            RETURN (SELECT COALESCE((SELECT s.title FROM JournalTitleAndContent s WHERE s.language_id = preferredLanguageId AND s.journal_id = entityId LIMIT 1),
            (SELECT s.title FROM JournalTitleAndContent s WHERE s.language_id = backupLanguageId AND s.journal_id = entityId LIMIT 1), (SELECT s.title FROM JournalTitleAndContent s WHERE s.journal_id = entityId LIMIT 1)));
        WHEN translationSubject = 'SOIL_TYPE' THEN
            RETURN (SELECT COALESCE((SELECT s.translatedName FROM SoilTypeNameTranslation s WHERE s.language_id = preferredLanguageId AND s.soiltypedetails_id = entityId LIMIT 1),
            (SELECT s.translatedName FROM SoilTypeNameTranslation s WHERE s.language_id = backupLanguageId AND s.soiltypedetails_id = entityId LIMIT 1), (SELECT s.translatedName FROM SoilTypeNameTranslation s WHERE s.soiltypedetails_id = entityId LIMIT 1)));
        WHEN translationSubject = 'COUNTRY' THEN
            RETURN (SELECT COALESCE((SELECT ct.translatedName FROM countryNameTranslation ct WHERE ct.parent_id = entityId AND ct.language_id = preferredLanguageId LIMIT 1),
            (SELECT ct.translatedName FROM countryNameTranslation ct WHERE ct.parent_id = entityId AND ct.language_id = backupLanguageId LIMIT 1), (SELECT ct.translatedName FROM countryNameTranslation ct WHERE ct.parent_id = entityId LIMIT 1)));
        WHEN translationSubject = 'PROVINCE' THEN
            RETURN (SELECT COALESCE((SELECT ct.translatedName FROM provinceNameTranslation ct WHERE ct.parent_id = entityId AND ct.language_id = preferredLanguageId LIMIT 1),
            (SELECT ct.translatedName FROM provinceNameTranslation ct WHERE ct.parent_id = entityId AND ct.language_id = backupLanguageId LIMIT 1), (SELECT ct.translatedName FROM provinceNameTranslation ct WHERE ct.parent_id = entityId LIMIT 1)));
        WHEN translationSubject = 'PLACE' THEN
            RETURN (SELECT COALESCE((SELECT ct.translatedName FROM placeNameTranslation ct WHERE ct.parent_id = entityId AND ct.language_id = preferredLanguageId LIMIT 1),
            (SELECT ct.translatedName FROM placeNameTranslation ct WHERE ct.parent_id = entityId AND ct.language_id = backupLanguageId LIMIT 1), (SELECT ct.translatedName FROM placeNameTranslation ct WHERE ct.parent_id = entityId LIMIT 1)));
        ELSE SIGNAL SQLSTATE '45000' SET MESSAGE_TEXT = 'Invalid enumType!';
    END CASE;
END

我在一个更大的选择查询中使用了这个函数。IESELECT c.scientificName, GET_TRANSLATION(@languageId, 1, j.soiltype_details_id, 'CROP') as soilType FROM journal j;

我错误地给它输入CROP而不是CROP_NAME. 现在它应该已经进入结构的else一部分CASE并返回错误消息invalid enumType。但是，我真正得到的是错误Error Code: 1265. Data truncated for column 'translationSubject' at row 1。

我的问题是；为什么它不触发我为无效枚举类型定义的错误，为什么它被translationSubject视为“截断”的列？这个错误完全不合适，因为原因仅仅是一个错误的枚举值。

谁能向我解释这种行为？

谢谢

编辑：

我只是尝试将 SIGNAL 更改为 RESIGNAL 并删除 SQLSTATE 参数。此外，我添加了

DECLARE EXIT HANDLER FOR SQLEXCEPTION
    BEGIN
        RESIGNAL;
    END;

到 GET_TRANSLATION 但同样的错误仍然存​​在。