mysql Max()函数实例 使用Max()函数计算最大值

mysql> CREATE TABLE Classes
    -> (
    ->     ClassID SMALLINT NOT NULL PRIMARY KEY,
    ->     Dept CHAR(4) NOT NULL,
    ->     Level ENUM('Upper', 'Lower') NOT NULL,
    ->     TotalStudents TINYINT UNSIGNED NOT NULL
    -> );
Query OK, 0 rows affected (0.00 sec)

mysql> INSERT INTO Classes VALUES
    -> (1001, 'ANTH', 'Upper', 25),
    -> (1002, 'ANTH', 'Upper', 25),
    -> (1003, 'MATH', 'Upper', 18),
    -> (1004, 'ANTH', 'Lower', 19),
    -> (1005, 'ENGL', 'Upper', 28),
    -> (1006, 'MATH', 'Lower', 23),
    -> (1007, 'ENGL', 'Upper', 25),
    -> (1008, 'MATH', 'Lower', 29),
    -> (1009, 'ANTH', 'Upper', 25),
    -> (1010, 'ANTH', 'Lower', 30),
    -> (1011, 'ENGL', 'Lower', 26),
    -> (1012, 'MATH', 'Lower', 22),
    -> (1013, 'ANTH', 'Upper', 27),
    -> (1014, 'ANTH', 'Upper', 21),
    -> (1015, 'ENGL', 'Lower', 25),
    -> (1016, 'ENGL', 'Upper', 32);
Query OK, 16 rows affected (0.00 sec)
Records: 16  Duplicates: 0  Warnings: 0

mysql> SELECT Dept, Level, MAX(TotalStudents) AS Maximum
    -> FROM Classes
    -> GROUP BY Dept, Level WITH ROLLUP; --//Max()函数求最大值
+------+-------+---------+
| Dept | Level | Maximum |
+------+-------+---------+
| ANTH | Upper |      27 |
| ANTH | Lower |      30 |
| ANTH | NULL  |      30 |
| ENGL | Upper |      32 |
| ENGL | Lower |      26 |
| ENGL | NULL  |      32 |
| MATH | Upper |      18 |
| MATH | Lower |      29 |
| MATH | NULL  |      29 |
| NULL | NULL  |      32 |
+------+-------+---------+
10 rows in set (0.00 sec)

mysql> drop table Classes;
Query OK, 0 rows affected (0.00 sec)