Cast(字段名 as 转换的类型)，其中类型可以为：

BINARY[(N)]
CHAR[(N)]
DATE
DATETIME
DECIMAL[(M[,D])]
SIGNED [INTEGER]
TIME
UNSIGNED [INTEGER]

用法:

SELECT CAST(ctime AS char) as new FROM user;

ctime是原列名, new是新列名

参考:

https://*.com/questions/12126991/cast-from-varchar-to-int-mysql