How can I query monthly cost data to display a proper time series in Grafana?

Below is one approach. Data Studio (or your dashboard tool) needs a clean query that returns a date field (for the X axis) and a numeric field (for the Y axis). You can achieve this by simply selecting from the underlying table without wrapping your query in a subquery. If you have one row per month then:

SQLCopied
SELECT 
  Month, 
  Cost
FROM 
  MyTable
ORDER BY 
  Month ASC

If your table contains several rows per month and you want to aggregate the costs, use:

SQLCopied
SELECT 
  Month, 
  SUM(Cost) AS TotalCost
FROM 
  MyTable
GROUP BY 
  Month
ORDER BY 
  Month ASC

This version ensures that your dashboard will have a continuous time series with the months on the abscissa and the total or individual costs on the ordinate.