准备：
表名：testscore
表字段及值
方法一：
SELECT name from testscore GROUP BY name HAVING min(score)>80
结果图：
方法二：
SELECT DISTINCT name from testscore where name not in (select name from testscore where score<80)
结果图：
方法三：
SELECT * from (SELECT name,min(score) 最小成绩 from testscore GROUP BY name) t where t.最小成绩>80
结果图：
