mysql查询不'；不能在存储过程中工作

这是我的存储过程：

CREATE DEFINER=`root`@`localhost` PROCEDURE `isUserValid`(IN `facebookId` VARCHAR(20), IN `userAccessToken` TEXT)
    NO SQL
    COMMENT 'check if user is valid. return true or false'
Begin
    /* declare the select resluts variables*/   
    Declare accessToken TEXT;
    Declare expires datetime;

    /* fill the variables with saved user's access token an expires time*/
    Select Access_Token, Expires
    Into accessToken, expires
    From Users Where Facebook_Id = facebookId;      

    select expires,accessToken;
    /* If the saved access token and expires are valid return true */
    If (BINARY accessToken = userAccessToken And expires > now()) Then
        select true As isUserValid;
    Else
        select false As isUserValid;
    End If; 
End

出于某种原因，查询：

/* fill the variables with saved user's access token an expires time*/
Select Access_Token, Expires
Into accessToken, expires
From Users Where Facebook_Id = facebookId;

将Expires始终返回为null

当我在过程之外运行相同的查询时-它将Expires作为值返回

我不明白怎么了…

好的，找到了， 必须为变量和字段提供不同的名称

my expires与表中的expires相同，因此它始终为空