How to unnest and pivot two columns in BigQuery

Question

Say I have a BQ table containing the following information

| id    | test.name     | test.score    |
|----   |-----------    |------------   |
| 1     | a                 


        

Answer 1

Conditional aggregation is a good approach. If your tables are large, you might find that this has the best performance:

select t.id,
       (select max(tt.score) from unnest(t.score) tt where tt.name = 'a') as a,
       (select max(tt.score) from unnest(t.score) tt where tt.name = 'b') as b,
       (select max(tt.score) from unnest(t.score) tt where tt.name = 'c') as c
from `table` t;

The reason I recommend this is because it avoids the outer aggregation. The unnest() happens without shuffling the data around -- and I have found that this is a big win in terms of performance.