原始问题：
创建一个存储过程，判断分数属于哪个层级
CREATE PROCEDURE CheckScoreLevel (IN Score INT)
BEGIN
DECLARE Level VARCHAR(20);
IF Score >= 90 THEN SET Level = 'A';
ELSEIF Score >= 80 THEN SET Level = 'B';
ELSEIF Score >= 70 THEN SET Level = 'C';
ELSEIF Score >= 60 THEN SET Level = 'D';
ELSE SET Level = 'Failed';
SELECT Level; END
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