Creating a new view in BigQuery, with case statements - google-bigquery

Question

I am trying to create a new view in BigQuery using some of the Google hosted data.
The data is for traffic collisions in New York.
For each unique day in the dataset, I want to find the borough and sum up some fields (people injured, killed, etc.)
Now, the dataset does have a borough field, but this is incomplete, and what I have seen is that there are also latitude and longitude fields. However these are also not complete.
So I see 3 scenarios.
The borough is set, use that
No borough, but there is lat and long, so use those in a sub query.
There is no lat, long or borough, so just enter an "unknown" here
to find the borough from lat and long, there is another public dataset, and I used this with a lat and long to check
SELECT UPPER(tz_loc.borough) FROM `bigquery-public-data.new_york_taxi_trips.taxi_zone_geom` tz_loc
WHERE (ST_DWithin(tz_loc.zone_geom, ST_GeogPoint(-73.94398, 40.680088),0))
and that seemed to work.
So I constructed my query like this:
CREATE VIEW `your-project-id.your_dataset_id.collisions_data_bourgh` AS
SELECT CAST(timestamp as DATE) as collision_date,
COUNT(CAST(timestamp as DATE)) as NUM_COLLISIONS,
CASE
WHEN ds.borough IS NOT NULL THEN CAST(borough as STRING) -- when the borough is set
WHEN ((ds.latitude IS NOT NULL or ds.longitude IS NOT NULL) AND ds.borough IS NULL) THEN (SELECT CAST(UPPER(tz_loc.borough)as STRING) FROM `bigquery-public-data.new_york_taxi_trips.taxi_zone_geom` tz_loc WHERE (ST_DWithin(tz_loc.zone_geom, ST_GeogPoint(CAST(ds.longitude AS FLOAT64), CAST(ds.latitude AS FLOAT64)),0))) -- when the borough is null and either lat or long is not null
WHEN (ds.latitude IS NULL OR ds.longitude IS NULL OR ds.borough IS NULL) THEN "Unknown"
END AS NEIGHBORHOOD,
SUM(CAST(number_of_cyclist_killed as INT64)) as CYCLISTS_KILLED,
SUM(CAST(number_of_cyclist_injured as INT64)) as CYCLISTS_INJURED,
SUM(CAST(number_of_motorist_killed as INT64)) as MOTORISTS_KILLED,
SUM(CAST(number_of_motorist_injured as INT64)) as MOTORISTS_INJURED,
SUM(CAST(number_of_pedestrians_killed as INT64)) as PEDS_KILLED,
SUM(CAST(number_of_pedestrians_injured as INT64)) as PEDS_INJURED,
SUM(CAST(number_of_persons_killed as INT64)) as PERSONS_KILLED,
SUM(CAST(number_of_persons_injured as INT64)) as PERSONS_INJURED,
FROM `bigquery-public-data.new_york_mv_collisions.nypd_mv_collisions` ds
GROUP BY collision_date, NEIGHBORHOOD;
And the query ran ok - however when I try to query the created view, I get an error
LEFT OUTER JOIN cannot be used without a condition that is an equality of fields from both sides of the join.
I cannot see where my error is, if it's in the logic, if it's in the way I've joined together things.

Answer 1

You encounter the LEFT OUTER JOIN error since you were not able to the two tables. You can join them in the WHERE clause of your subquery. Adding AND tz_loc.borough = ds.borough at your subquery should make it work.
See working query:
CREATE VIEW `your-project-id.your_dataset_id.collisions_data_bourgh` AS
SELECT
CAST(timestamp AS DATE) AS collision_date,
COUNT(CAST(timestamp AS DATE)) AS NUM_COLLISIONS,
CASE
WHEN ds.borough IS NOT NULL THEN CAST(borough AS STRING) -- when the borough is set
WHEN ((ds.latitude IS NOT NULL or ds.longitude IS NOT NULL) AND ds.borough IS NULL)
THEN (
SELECT CAST(UPPER(tz_loc.borough)as STRING)
FROM bigquery-public-data.new_york_taxi_trips.taxi_zone_geom tz_loc
WHERE
ST_DWithin(tz_loc.zone_geom,
ST_GeogPoint(CAST(ds.longitude AS FLOAT64),
CAST(ds.latitude AS FLOAT64)),0)
AND tz_loc.borough = ds.borough
)
WHEN (ds.latitude IS NULL
OR ds.longitude IS NULL
OR ds.borough IS NULL) THEN "Unknown"
END
AS NEIGHBORHOOD,
SUM(CAST(number_of_cyclist_killed AS INT64)) AS CYCLISTS_KILLED,
SUM(CAST(number_of_cyclist_injured AS INT64)) AS CYCLISTS_INJURED,
SUM(CAST(number_of_motorist_killed AS INT64)) AS MOTORISTS_KILLED,
SUM(CAST(number_of_motorist_injured AS INT64)) AS MOTORISTS_INJURED,
SUM(CAST(number_of_pedestrians_killed AS INT64)) AS PEDS_KILLED,
SUM(CAST(number_of_pedestrians_injured AS INT64)) AS PEDS_INJURED,
SUM(CAST(number_of_persons_killed AS INT64)) AS PERSONS_KILLED,
SUM(CAST(number_of_persons_injured AS INT64)) AS PERSONS_INJURED,
FROM
bigquery-public-data.new_york_mv_collisions.nypd_mv_collisions ds
GROUP BY
collision_date,
NEIGHBORHOOD
Snippet of the whole SELECT clause:
Created View: