mysql round()函数以及convert()函数，保留n位小数

mysql> select round(2.232,);
+----------------+
| round(2.232,) |
+----------------+
|           2.23 |
+----------------+
 row in set (0.00 sec)

mysql> select convert(1.2323,decimal(,));
+------------------------------+
| convert(1.2323,decimal(,)) |
+------------------------------+
|                         1.23 |
+------------------------------+
 row in set (0.00 sec)