mysql的ifelse怎么yong

这个怎么用mysql实现？

CREATE TRIGGER tri_UPDATE_DELETE_SC
on SC
FOR UPDATE, DELETE
AS
--检测成绩列表是否被更新
IF UPDATE(Grade)
    BEGIN
    --显示学号、课程号、原成绩和新成绩信息
    SELECT INSERTED.cno, DELETED.grade AS 原成绩,
    INSERTED.grade AS 新成绩
    FROM DELETED, INSERTED
    WHERE DELETED.sno=INSERTED.sno
    END
--检测是更新还是删除操作
ELSE IF COLUMNS_UPDATED()=0
BEGIN
    --显示被删除的学号、课程号和成绩信息
    SELECT 被删除的学号=DELETED.sno, DELETED.cno, DELETED.grade AS 原成绩
    FROM DELETED
END
ELSE
    --返回提示信息
PRINT '更新了非成绩列！'

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