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2208/天天乐学考试答案/MySQL练习（一）.md

@@ -302,3 +302,25 @@ END $$
 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;
+```
+