mysql不支持 EXCEPT . 我想你有个用处：

SELECT ds.playerid, ds.playername, ds.minerals, ds.daydate
FROM dailyscore ds
WHERE daydate = '".$yesterday."' AND
      NOT EXISTS (SELECT 1
                  FROM dailyscore
                  WHERE ds2.playerid = ds.playerid AND
                        ds2.minerals = ds.minerals AND
                        ds2.daydate = '".$twodays."'
                 )
ORDER BY ds.minerals DESC;

注意：您不应该通过mung字符串来传递参数。您应该学会正确地传递参数，使用占位符，例如 ? .

不需要像except或minus这样的set运算符。将两天的分数相加，计算出每日分数的差值：

SELECT playerid, playername, minerals
FROM (
    SELECT ds_yesterday.playerid,
        ds_yesterday.playername,
        CASE
            WHEN ds_twodays.minerals IS NULL
            THEN ds_yesterday.minerals
            ELSE ds_yesterday.minerals - ds_twodays.minerals
        END minerals
    FROM dailyscore as ds_yesterday
    LEFT JOIN dailyscore as ds_twodays ON 
        ds_twodays.playerid = ds_yesterday.playerid
        AND ds_twodays.daydate = '2018-08-07'
    WHERE ds_yesterday.daydate = '2018-08-08'
) scoredifference
ORDER BY minerals DESC;

您可以使用这个sql并将其放入php代码中。日期应该被存储在php变量中的值替换。