$__timeGroup(...., auto) fails for shorter time spans

[ptomasroos]

Bug Report

Using auto interval calculation fails for a 30 minutes selected time interval
Its not grouping it correctly since there are more rows than the LIMIT causing the graph to be empty at the end

Expected Behavior

A full graph in the display

Actual Behavior

Missing data for the last few seconds

Steps to Reproduce the Problem

1. Render a graph with using $__timeGroup(..., auto)
2. Select last 30 minutes

Specifications

• Version: 1.0.7

Extra

Here are my two timestamps used in this example.

(1587534441900-1587532641900)/1000/60 = 30 minutes.

(1587534441900-1587532641900)/1000 = 1800 seconds.

The LIMIT passed is 1742.

Example query from the inspector.

SELECT
  TIMESTAMP_SECONDS(DIV(UNIX_SECONDS(`timestamp`), 1) * 1) AS time,
  COUNT(*) AS count
FROM
  ``
WHERE
  `timestamp` BETWEEN TIMESTAMP_MILLIS (1587532641900)
  AND TIMESTAMP_MILLIS (1587534441900)
GROUP BY
  1
ORDER BY
  1
LIMIT
  1742

Clearly 1800 points can never fit into 1742. 1742 comes from the max data points.
Same problem arises up to last 12 hours, where its flatting out because its doing larger time slices.

So either we need to in those cases skip the maxDataPoint value and increase it or, rather we need to make a bucket which can't be a single second it would rather be 1.033 seconds in this case, not sure how the sql expression would support that. Or the best, it would require a group of 2 seconds when there's a overflow, instead of 1 second which its grouped at currently