继续学习MySQL，这篇记录下conv函数。conv函数用于数字的进制转换，共有三个参数：
CONV(N,from_base,to_base)
N是要转换的数据，from_base是原进制，to_base是目标进制。
select conv(16,10,16);
+----------------+
| conv(16,10,16) |
+----------------+
| 10 |
+----------------+
1 row in set (0.04 sec)
+----------------+
| conv(16,10,16) |
+----------------+
| 10 |
+----------------+
1 row in set (0.04 sec)
如果N是有符号数字，则to_base要以负数的形式提供，否则会将N当作无符号数
mysql> select conv(-16,10,16);
+------------------+
| conv(-16,10,16) |
+------------------+
| FFFFFFFFFFFFFFF0 |
+------------------+
1 row in set (0.00 sec)
mysql> select conv(-16,10,-16);
+------------------+
| conv(-16,10,-16) |
+------------------+
| -10 |
+------------------+
1 row in set (0.00 sec)
+------------------+
| conv(-16,10,16) |
+------------------+
| FFFFFFFFFFFFFFF0 |
+------------------+
1 row in set (0.00 sec)
mysql> select conv(-16,10,-16);
+------------------+
| conv(-16,10,-16) |
+------------------+
| -10 |
+------------------+
1 row in set (0.00 sec)
除了conv，还有几个特定进制转换的函数，如：
- hex(N)相当于conv(N,10,16)
- oct(N)相当于conv(N,10,8)
- bin(N)相当于conv(N,10,2)
另外还有一个convert函数用于转换不同的数据类型的，不要和conv搞混淆了。
