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   | mysql> describe stu; +-------+---------+------+-----+---------+----------------+ | Field | Type    | Null | Key | Default | Extra          | +-------+---------+------+-----+---------+----------------+ | id    | int(11) | NO   | PRI | NULL    | auto_increment | | name  | char(1) | YES  |     | NULL    |                | | age   | int(11) | YES  |     | NULL    |                | | grade | int(11) | YES  |     | NULL    |                | +-------+---------+------+-----+---------+----------------+ 4 rows in set (0.00 sec)
  mysql> select * from stu; +----+------+------+-------+ | id | name | age  | grade | +----+------+------+-------+ |  1 | a    |   11 |     1 | |  2 | b    |   12 |     1 | |  3 | c    |   13 |     1 | |  4 | d    |   11 |     2 | |  5 | e    |   12 |     2 | |  6 | f    |   13 |     2 | +----+------+------+-------+ 6 rows in set (0.00 sec)
  mysql> select max(name), max(age),grade from  stu group by grade; +-----------+----------+-------+ | max(name) | max(age) | grade | +-----------+----------+-------+ | c         |       13 |     1 | | f         |       13 |     2 | +-----------+----------+-------+ 2 rows in set (0.01 sec)
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