Case list

Trigger an alarm when the error 500 percentage increases rapidly

Count the percentage of error 500 every minute. An alarm is triggered when the percentage exceeds 40% in the last five minutes. 
status:500 | select __topic__, max_by(error_count,window_time)/1.0/sum(error_count) as error_ratio, sum(error_count) as total_error from (
select __topic__, count(*) as error_count , __time__ - __time__ % 300 as window_time from log group by __topic__, window_time)
group by __topic__ having max_by(error_count,window_time)/1.0/sum(error_count) > 0.4 and sum(error_count) > 500 order by total_error desc limit 100

Trigger an alarm when traffic decreases sharply

Count the traffic every minute. An alarm is triggered when traffic decreases sharply recently. Data in the last one minute does not cover a full minute. Therefore, divide the statistical value by (max(time) - min(time)) for normalization to count the average traffic per minute. 
* | SELECT SUM(inflow) / (max(__time__) - min(__time__)) as inflow_per_minute, date_trunc('minute',__time__) as minute group by minute

Calculate the average latency of each bucket set by data interval

* | select avg(latency) as latency , case when originSize < 5000 then 's1' when originSize < 20000 then 's2' when originSize < 500000 then 's3' when originSize < 100000000 then 's4' else 's5' end as os group by os

Return percentages in GROUP BY results

List the count results of different departments and the related percentages. This query combines subquery and window functions. sum(c) over() indicates to calculate the sum of values in all rows. 

* | select department, c*1.0/ sum(c) over () from(select count(1) as c, department from log groupby department)

Count the number of logs that meet the query condition

We must count the URLs by characteristics.In this situation, use the CASE WHEN syntax. You can also use the count_if syntax, which is simpler. 
* | select count_if(uri like '%login') as login_num, count_if(uri like '%register') as register_num, date_format(date_trunc('minute', __time__), '%m-%d %H:%i') as time group by time order by time limit 100