mysql更新表某字段值，使其等于前7条记录的汇总值，如何写sql？

[游北亮]

有一个下载量表，有日期、当日下载 和 近7天下载 这3个字段，
现在当日下载已经有数据了，请问如何更新 近7天下载 这个字段呢？

SqlServer里的SQL语句可以这么写实现，如：

UPDATE a SET a.down7=(
    SELECT SUM(down) FROM downData b WHERE b.ndate<=a.ndate AND b.ndate>dateadd(d, -7,a.ndate)
)
FROM downData a 

同样的set a.down7=(select )
这种语法放MySql里，就出错了， 求大师指点，MySql里如何更新？？？

[道玄希言]

查询语句：

SELECT t1.*,
(SELECT SUM(down) FROM downData 
WHERE ndate<t1.ndate AND ndate>=DATE_ADD(t1.ndate, INTERVAL -7 DAY)) AS mdown
FROM downData AS t1
ORDER BY ndate

[道玄希言]

更新语句大概可以这么写：

UPDATE downData AS t
INNER JOIN
(SELECT tt.ndate,
(SELECT SUM(down) FROM downData  
WHERE ndate <= tt.ndate AND ndate >= 
DATE_ADD(tt.ndate, INTERVAL -6 DAY)) AS mds
FROM downData AS tt
) AS ttt  
ON ttt.ndate=t.ndate
SET t.down7=ttt.mds

[游北亮]

感谢，怎么就忘记可以在Select里内嵌子查询了

引用 2 楼 yangb0803 的回复:

更新语句大概可以这么写：

UPDATE downData AS t
INNER JOIN
(SELECT tt.ndate,
(SELECT SUM(down) FROM downData  
WHERE ndate <= tt.ndate AND ndate >= 
DATE_ADD(tt.ndate, INTERVAL -6 DAY)) AS mds
FROM downData AS tt
) AS ttt  
ON ttt.ndate=t.ndate
SET t.down7=ttt.mds