MySQL 的CAST()和CONVERT()函数可用来获取一个类型的值,并产生另一个类型的值。两者具体的语法如下:
CAST(value as type);
CONVERT(value, type);
就是CAST(xxx AS 类型), CONVERT(xxx,类型)。
mysql> SELECT CAST('3.35' AS signed);
+------------------------+
| CAST('3.35' AS signed) |
+------------------------+
| 3 |
+------------------------+
1 row in set
可以转换的类型是有限制的。这个类型可以是以下值其中的一个:
下面举几个例子:
例一
mysql> SELECT CONVERT('23',SIGNED);
+----------------------+
| CONVERT('23',SIGNED) |
+----------------------+
| 23 |
+----------------------+
1 row in set
例二
mysql> SELECT CAST('125e342.83' AS signed);
+------------------------------+
| CAST('125e342.83' AS signed) |
+------------------------------+
| 125 |
+------------------------------+
1 row in set
例三
mysql> SELECT CAST('3.35' AS signed);
+------------------------+
| CAST('3.35' AS signed) |
+------------------------+
| 3 |
+------------------------+
1 row in set
像上面例子一样,将varchar 转为int 用 cast(a as signed),其中a为varchar类型的字符串。