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2208/天天乐学考试答案/MySQL练习（一）.md

@@ -305,6 +305,53 @@ DELIMITER ;
 ### 第四套
 
 ```sql
+#1
+ALTER TABLE tb_students MODIFY gender ENUM('男', '女', '未知');
+#2
+ALTER TABLE tb_scores MODIFY score FLOAT(7, 2);
+#3
+CREATE TABLE tb_scores_bak1 AS
+SELECT *
+FROM tb_scores;
+#4
+UPDATE test1 t1, (
+	SELECT tname, CONCAT(tname,'@',COUNT(*)) str
+	FROM test1
+	GROUP BY tname
+	HAVING COUNT(*) IN (3, 4)
+)t2
+SET t1.tname = t2.str
+WHERE t1.tname = t2.tname;
+
+#5
+SELECT *
+FROM tb_courses c
+ORDER BY c.cid+0
+LIMIT 4, 11;
+
+#6
+SELECT s.stuname, TIMESTAMPDIFF(YEAR,s.birthday,'2023-12-01')
+FROM tb_students s
+WHERE TIMESTAMPDIFF(YEAR,s.birthday,'2023-12-01') BETWEEN 30 AND 40;
+
+#7
+SELECT st.stuname, st.gender, st.birthday, c.cname, sc.score,
+	IF(sc.score >= 90, '优秀', 
+	IF(sc.score >= 80, '良好', 
+	IF(sc.score >= 70, '中等', 
+	IF(sc.score >= 60, '及格', '不及格'))))
+FROM tb_students st, tb_scores sc, tb_courses c
+WHERE st.stuid = sc.student_id AND sc.course_id = c.cid
+ORDER BY sc.score DESC;
+
+#8
+CREATE VIEW v_scores AS
+SELECT c.cname, CEIL(AVG(sc.score)), MAX(sc.score), MIN(sc.score)
+FROM tb_students st, tb_scores sc, tb_courses c
+WHERE st.stuid = sc.student_id AND sc.course_id = c.cid
+GROUP BY c.cid;
+
+#9
 DELIMITER $$
 CREATE TRIGGER tri_updateAgeGroup
 BEFORE UPDATE ON tb_students