mysql-php Statistics 7th Retention rate

Database about more than 50,000 login details data, how to check the table statistics 7th retention rate is relatively high?

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Database about more than 50,000 login details data, how to check the table statistics 7th retention rate is relatively high?

The combination of registered array key values for datetime date format;
For example: 2016-08-11

$arr = [    '2016-08-11' => [2,3,5,6,111,333,23],//存储当天注册的用户id    '2016-08-12' => [],    ....]

Check the retention rate of users in 2016-08-11

 select count(*) from operation_log where client_id in() and login_time bewteen 1 and 2

Number of logins in 2016-08-17/2016-08-11 Login users = retention rate

More than 50,000 how to do it, direct PHP array processing will not consume too much memory.
You can also consider storing intermediate results with memcache or Redis.

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