Apache - Requests to rare files

Original query, unchanged.

let lb_period_start = 14d;
let lb_period_end = 1d;
let known_files = ApacheHTTPServer
| where TimeGenerated between (ago(lb_period_start) .. ago(lb_period_end))
| extend File = extract(@"(.*\/)?(.*)", 2, tostring(UrlOriginal))
| summarize makeset(File);
ApacheHTTPServer
| where TimeGenerated > ago(24h)
| extend File = extract(@"(.*\/)?(.*)", 2, tostring(UrlOriginal))
| where File in~ (known_files)
| extend FileCustomEntity = File, UrlCustomEntity = UrlOriginal