1.GROUP_CONCAT()

SELECT   t.gradeName ,GROUP_CONCAT(t.stuName)FROM t_student    t    GROUP BY  t.gradename

2.COUNT()

SELECT   t.gradeName ,COUNT(t.stuName) FROM t_student t  GROUP BYt.gradename

3.HAVING COUNT(t.stuName)>3

SELECT   t.gradeName ,COUNT(t.stuName) FROM t_student t  GROUP BY t.gradenameHAVING COUNT(t.stuName)>3

4.LIMIT  

SELECT * FROM t_student LIMIT  0,5