I faced this issue before, I also tried in company I worked for to send alert based on bigquery database when condition met

I tried Pub Sub, App Script, Collab, but non of them provide simple and comprehensive solution, and you need to create all the flow by yourself, create the email sending code, condition exc' it's taking a lot of time and really hard to scale up.

So, I've simple solution for you, Analytics Model platform ( Disclaimer: I'm working in Analytics Model)
Here you can find tutorial, explain step by step how to set up an automated alert.

Anyway I will explain step by step how to set up an automated alert:

You need to go to Connection, select Bigquery
Add your table
Create your Insight (what you need to be triger), make sure you're using the your Bigquery table
Add to your feed
Go to your feed and schedule the mail and the condition