什么是留存比率?

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select * from tbl_Articles WHERE ArticleID=396276 LIMIT 0,1
select * from tbl_Articles_data WHERE ArticleID=396276 LIMIT 0,1
select * from tbl_Articles_sphinx where id=396276 LIMIT 0,1
SELECT ArticleID,Title FROM tbl_Articles WHERE ArticleID IN(3490459,3507071,1401633,542468,808208,3157215,1028800,557432,535602,3066539,2765216,3191289,1184241,2545481,519108,784612,3388525,893101,554063,596214,1809400,732607,1314298,2657980,1013798,2350029,874367,579369,496487,514406) ORDER BY field (ArticleID,3490459,3507071,1401633,542468,808208,3157215,1028800,557432,535602,3066539,2765216,3191289,1184241,2545481,519108,784612,3388525,893101,554063,596214,1809400,732607,1314298,2657980,1013798,2350029,874367,579369,496487,514406)