MYSQL完全手册学习笔记（第七章）
MYSQL函数

mysql> select round(10.33),round(64.50001),round(10.98547);
+--------------+-----------------+-----------------+
| round(10.33) | round(64.50001) | round(10.98547) |
+--------------+-----------------+-----------------+
|           10 |              65 |              11 |
+--------------+-----------------+-----------------+
1 row in set (0.00 sec)

Round 函数四舍五入



mysql> select truncate(1.78502356,3),truncate(-6235.3256984,10);
+------------------------+----------------------------+
| truncate(1.78502356,3) | truncate(-6235.3256984,10) |
+------------------------+----------------------------+
|                  1.785 |           -6235.3256984000 |
+------------------------+----------------------------+
1 row in set (0.00 sec)

mysql> select truncate(1789.09854,-2),truncate(-629.6953245,-1);
+-------------------------+---------------------------+
| truncate(1789.09854,-2) | truncate(-629.6953245,-1) |
+-------------------------+---------------------------+
|                    1700 |                      -620 |
+-------------------------+---------------------------+
1 row in set (0.00 sec)


Truncate 把一个数字截短成为一个指定小数个数的数字，注意取负数的时候哦

mysql> select abs (-789);
+------------+
| abs (-789) |
+------------+
|        789 |
+------------+
1 row in set (0.00 sec)

Abs绝对值


mysql> select * from toys;
+----+-----------------+-------+-------+-------+----------+
| id | item            | ctm   | ctr   | ctc   | quantity |
+----+-----------------+-------+-------+-------+----------+
|  0 | ww              |  3.00 |  3.00 |  3.00 |      200 |
|  1 | huggy bear      |  5.00 |  7.40 |  9.90 |      300 |
|  2 | coloring book   |  3.00 |  5.00 |  7.99 |     2000 |
|  3 | board game      | 12.00 | 20.00 | 39.90 |     1430 |
|  4 | activity cd-rom |  2.00 |  6.00 | 17.49 |     3780 |
|  6 | ww              |  6.00 |  6.00 |  6.00 |      100 |
+----+-----------------+-------+-------+-------+----------+
6 rows in set (0.00 sec)

mysql> select * from toys group by item;
+----+-----------------+-------+-------+-------+----------+
| id | item            | ctm   | ctr   | ctc   | quantity |
+----+-----------------+-------+-------+-------+----------+
|  4 | activity cd-rom |  2.00 |  6.00 | 17.49 |     3780 |
|  3 | board game      | 12.00 | 20.00 | 39.90 |     1430 |
|  2 | coloring book   |  3.00 |  5.00 |  7.99 |     2000 |
|