[*] Fix global-db-overview query logic, fixes #1152

[Mazen050]

This PR partially fixes #1152

Fixing query logic in the global-db-overview dashboard.

[pashagolub]

closed by #1262

[Mazen050]

@pashagolub this PR has nothing to do with my PR. My PR fixes another bug

[pashagolub]

@Mazen050 sorry about that!

[Mazen050]

Before:

After:

[0xgouda]

Please describe how you fixed the queries.

[Mazen050]

Hello @0xgouda , Based on your fix I fixed the queries my self first then sent to gemini 3 for review.

Here basically we get the most recent sample before the dashboards selected time range so that lag() has something to subtract from for the first row in the range. preventing the NULL we used to get because the inner query's WHERE time >= $__timeFrom() excludes any prior row for it to look back at.

A new addition to your CTE is DISTINCT ON (dbname) which is necessary here because in this dashboard the queries run on multiple dbs so DISTINCT ON (dbname) makes us select the most recent rows(before range) per db.

Please if anything else needs more clarification let me know.

[Mazen050]

I rebased and now go tests are failing.