grafana 绘图

https://stackoverflow.com/questions/65953252/grafana-timeseries-chart-from-mysql-json-data
https://stackoverflow.com/questions/54771946/grafana-sql-query-convert-string-to-number

1. 曲线图，基于时序数据
   SELECT UNIX_TIMESTAMP(created_at) as time_sec,
   CAST(metric_value as SIGNED integer) as value,
   'Metric Value' as metric
   FROM lumenis_db.telemetry
   WHERE $__timeFilter(created_at)