怎样计算平均数和方差简便

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select * from tbl_Articles WHERE ArticleID=309996 LIMIT 0,1
select * from tbl_Articles_data WHERE ArticleID=309996 LIMIT 0,1
select * from tbl_Articles_sphinx where id=309996 LIMIT 0,1
SELECT ArticleID,Title FROM tbl_Articles WHERE ArticleID IN(4173328,4152709,4152599,4152583,4152556,4152541,4152540,4134240,4077412,3970122,3958100,3901108,3829702,3818258,3793978,3774571,3770474,3770447,3731331,3728884,3715487,3671186,3671177,3671073,3606440,3577106,3576169,3576146,3573540,3572349) ORDER BY field (ArticleID,4173328,4152709,4152599,4152583,4152556,4152541,4152540,4134240,4077412,3970122,3958100,3901108,3829702,3818258,3793978,3774571,3770474,3770447,3731331,3728884,3715487,3671186,3671177,3671073,3606440,3577106,3576169,3576146,3573540,3572349)