计算用户的平均次日留存率
https://www.nowcoder.com/practice/126083961ae0415fbde061d7ebbde453
with tmp as (select distinct device_id,date from question_practice_detail order by device_id,date) select (select count(t2.device_id) from tmp t1 left join tmp t2 on t1.device_id = t2.device_id and datediff(t2.date,t1.date) = 1 ) / count(device_id) from tmp;
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const flattern = (obj) => {
const res = {};
const dfs = (curr, path) => {
if(typeof curr === 'object' && curr !== null) {
const isArray = Array.isArray(curr);
for(let key in curr) {
const newPath = path ? isArray ? `${path}[${key}]` : `${path}.${key}` : key;
dfs(curr[key], newPath);
}
} else {
res[path] = curr
}
}
dfs(obj);
return res;
}
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