比如一个学生表,要查找出年级,班级这两个不同字段的组合,用下面两种方式的结果是一样的,请问哪种方式比较快?
select distinct grade,class from student
select grade,class from student group by grade,class
select distinct grade,class from student
select grade,class from student group by grade,class
调试欢乐多
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