How can I get result in JSON format from AWS Athena? - sql

Question

I want to get result in JSON format, below is the structure of object obj
UUID string
MobileCountryCode string
UserState []struct {
Mobile int64
IsNewUser bool
}
when i do simple select of object from Athena via Redash:
select obj FROM table_name
getting output in this format:
{uuid=UCLPKJWPZXH,mobile_country_code=,user_state=[{mobile=9988998899, is_new_user=false}]}
We can see clearly the output doesn't contain double quotes for json keys and has = instead of : to qualifier for proper json
I even tried casting it to json:
select CAST(obj AS JSON) AS json_obj FROM table_name
but i am getting only values without json keys like below:
["UCLPKJWPZXH","",[["9988998899",false]]]
But i want it to be like this with json keys
{"uuid":"UCLPKJWPZXH","mobile_country_code":"","user_state":[{"mobile":9988998899,"is_new_user":false}]}

Answer 1

Athena is based on Presto/Trino (engine v3 should use Trino functions) and in Trino cast(... as json) should work:
select cast(r as json)
from (values (1, CAST(ROW('UUID123', array[row(1, TRUE)]) AS ROW(UUID varchar, UserState array(row(Mobile int, IsNewUser boolean)))))) as t(id, r);
Output:
_col0
----------------------------------------------------------------
{"uuid":"UUID123","userstate":[{"mobile":1,"isnewuser":true}]}
Try upgrading to v3 engine. If you are already using v3 engine or it does not work after upgrade or you can't upgrade - the only way is to convert ROW into MAP, cause Presto treats ROWs as arrays (docs):
When casting from ROW to JSON, the result is a JSON array rather than a JSON object. This is because positions are more important than names for rows in SQL.
And converting row to map can be quite cumbersome:
select cast(
map(array['UUID123', 'MobileCountryCode', 'UserState'],
array[
cast(r.UUID as json),
cast(r.MobileCountryCode as json),
cast(
transform(r.UserState,
e -> map(
array['Mobile', 'IsNewUser'],
array[cast(e.Mobile as json), cast(e.IsNewUser as json)]))
as json)
])
as json)
from (values (1, CAST(ROW('UUID123', 'US', array[row(1, TRUE)]) AS ROW (UUID varchar, MobileCountryCode varchar,
UserState array(row(Mobile int, IsNewUser boolean)))))) as t(id, r);
Output:
_col0
--------------------------------------------------------------------------------------------
{"MobileCountryCode":"US","UUID123":"UUID123","UserState":[{"IsNewUser":true,"Mobile":1}]}