SQL: converting rows into columns

Question

I currently have a table that looks like the following:

user_id	device_id	device_type
12_aa	1245	mobile
15_ab	8909	tablet
17-ya	9090	mobile
18-ac	8900	desktop

I am trying to convert this table to below:

user_id	mobile	tablet	desktop
12_aa	1245	null	null
15_ab	null	8909	null
17_ya	9090	null	null
18_ac	null	null	8900

Could you help how this can be achieved?

Answer 1

Use below

select * from `project.dataset.table`
pivot (max(device_id) for device_type in ('mobile', 'tablet', 'desktop'))                    

If applied to sample data in your question - output is

Answer 2

You can use conditional aggregation:

select user_id,
       max(case when device_type = 'mobile' then device_id end) as mobile,
       max(case when device_type = 'tablet' then device_id end) as tablet,
       max(case when device_type = 'desktop' then device_id end) as desktop
from t
group by user_id;