CAST (expr AS type)BINARY # 二进制字符串
CHAR(n) # 普通字符串
DATE # 日期字符串
DATETIME # 时间日期字符串
DECIMAL(m,n) # 精确浮点数
SIGNED # 整数（有正负）
TIME # 时间字符串
UNSIGNED # 整数（正数）MySQL> select cast('25' as signed);
+----------------------+
| cast('25' as signed) |
+----------------------+
| 25 |
+----------------------+
