Bigquery SQL extract text left of the string

Question

I have this data below which is Quarters or Years. How do I in SQL legacy rewrite it so it can show?

RAW Data:

1. Q2M4_20/21
2. Q3M2_20/21
3. Q1M4_18/19
4. Q1_18/19_Actuals
5. Q1_18/19_Budgets

Goal (Result needed):

1. FY20_Q2M4
2. FY20_Q3M2
3. FY18_Q1M4
4. FY18_Q1_Actuals
5. FY18_Q1_Budget

NOTE: I would like the sql to also do the following:

1. Reorganize from QQ_YY to YY_QQ
2. Remove "/##" the forward slash and the two digits after
3. Add text "FY" before the "YY_QQ

I tried CHARINDEX My error message states "2.10 - 2.23: Unrecognized function charindex"

Thanks for looking into this.

Answer 1

Below is for BigQuery Standard SQL

select line, 
  format('FY%s_%s%s', 
    split(parts[offset(1)], '/')[offset(0)], 
    parts[offset(0)], 
    ifnull('_' || parts[safe_offset(2)], '')
  ) as result
from `project.dataset.table`,
unnest([struct(split(line, '_') as parts)])    

if applied to sample data from your question - output is