如Cast 函数和运算符:

结果的类型可以是以下值之一:

The type for the result can be one of the following values:

• BINARY[(N)]
• CHAR[(N)]
• 日期
• 日期时间
• 十进制[(M[,D])]
• SIGNED [INTEGER]
• TIME
• UNSIGNED [INTEGER]

因此，您应该使用:

SELECT CAST(PROD_CODE AS UNSIGNED) FROM PRODUCT