Explore the possibility of migrating to TiDB

[Rustin170506]

Feature Request

• I have searched the issues of this repository and believe that this is not a duplicate.

Is your feature request related to a Issue or PR(Optional)

None.

Describe the feature you'd like:

We can probably migrate devstats to TiDB.

We need to investigate what is incompatible and unsupported and find solutions.

Do you have any ideas on how to implement it?(Optional)

[Mini256]

pgsql supports the percentile_disc function that used to return the first input value whose position in the ordering equals or exceeds the specified fraction.

TiDB supports the PERCENT_RANK() windows function, but there does not seem to be a function called PERCENT_VALUE() for now.

Related SQL：

devstats/devstats/metrics/shared/opened_to_merged.sql

Line 38 in ae32704

select

select
  'open2merge;All;p15,med,p85' as name,
  percentile_disc(0.15) within group (order by open_to_merge asc) as open_to_merge_15_percentile,
  percentile_disc(0.5) within group (order by open_to_merge asc) as open_to_merge_median,
  percentile_disc(0.85) within group (order by open_to_merge asc) as open_to_merge_85_percentile
from
  tdiffs

[ti-chi-bot]

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[ti-chi-bot]

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