Convert ARRAY<STRUCT> to multiple columns in BigQuery SQL - sql

Question

I'm trying to convert Array< struct > to multiple columns.
The data structure looks like:
column name: Parameter
[
-{
key: "Publisher_name"
value: "Rubicon"
}
-{
key: "device_type"
value: "IDFA"
}
-{
key: "device_id"
value: "AAAA-BBBB-CCCC-DDDD"
}
]
What I want to get:
publisher_name device_type device_id
Rubicon IDFA AAAA-BBBB-CCCC-DDDD
I have tried this which caused the duplicates of other columns.
select h from table unnest(parameter) as h
BTW, I am very curious why do we want to use this kind of structure in Bigquery. Can't we just add the above 3 columns into table?

Answer 1

Below is for BigQuery Standard SQL
#standardSQL
SELECT
(SELECT value FROM UNNEST(Parameter) WHERE key = 'Publisher_name') AS Publisher_name,
(SELECT value FROM UNNEST(Parameter) WHERE key = 'device_type') AS device_type,
(SELECT value FROM UNNEST(Parameter) WHERE key = 'device_id') AS device_id
FROM `project.dataset.table`
You can further refactor code by using SQL UDF as below
#standardSQL
CREATE TEMP FUNCTION getValue(k STRING, arr ANY TYPE) AS
((SELECT value FROM UNNEST(arr) WHERE key = k));
SELECT
getValue('Publisher_name', Parameter) AS Publisher_name,
getValue('device_type', Parameter) AS device_type,
getValue('device_id', Parameter) AS device_id
FROM `project.dataset.table`

Answer 2

To convert to multiple columns, you will need to aggregate, something like this:
select ?,
max(case when pv.parameter = 'Publisher_name' then value end) as Publisher_name,
max(case when pv.parameter = 'device_type' then value end) as device_type,
max(case when pv.parameter = 'device_id' then value end) as device_id
from t cross join
unnest(parameter) pv
group by ?
You need to explicitly list the new columns that you want. The ? is for the columns that remain the same.