CAST (expr AS type)

BINARY          #  二進制字符串
CHAR(n)         #  普通字符串
DATE            #  日期字符串
DATETIME        #  時間日期字符串
DECIMAL(m,n)    #  精確浮點數
SIGNED          #  整數（有正負）
TIME            #  時間字符串
UNSIGNED        #  整數（正數）

mysql> select cast(‘25‘ as signed);
+----------------------+
| cast(‘25‘ as signed) |
+----------------------+
|                   25 |
+----------------------+