Bigquery - Average between columns ignoring NULL values

Question

TL;DR: Is there an easy way to calculate the average between a group of columns on google's bigquery?

I have a table with many estimates from a continuous variable, I'm giving an example with only three columns but the original table have something between 8 columns:

Estimate_A	Estimate_B	Estimate_C
4	2	3
1	2	2
4	NULL	2
2	3	NULL
4	NULL	NULL

I want to produce a new column AVG_ESTIMATE which is an AVERAGE between these estimate columns but ignoring the NULL data

Estimate_A	Estimate_B	Estimate_C	AVG_ESTIMATE
4	2	3	3
1	2	2	1.66
4	NULL	2	3
2	3	NULL	2.5
4	NULL	NULL	4

Answer 1

Consider below solution

select *, 
  (select round(avg(Estimate), 2) 
  from unnest([Estimate_A, Estimate_B, Estimate_C]) Estimate
  ) as AVG_ESTIMATE
from `project.dataset.table`    

If applied to sample data in your question - output is