Why is my SQL aliasing not being recognized? - sql

Question

This may be an incredibly simple question, but I'm not seeing what the problem here is. I'm trying to teach myself SQL and was working on an experiment to play with subqueries and aliasing. When I try to enter the following query (into BigQuery), I get an error message "Unrecognized name: cast1 at [3:1]" which persists even if I copy the COUNT lines into the outer query. Obviously there is something I'm not understanding about aliasing here, but I'm not sure where I am going wrong. I would appreciate any help from more experienced SQL users out there on how to improve, thank you in advance!
SELECT
cast__1_,
cast1 + cast2 + cast3 + cast4 AS num_films,
(
SELECT
cast__1_,
COUNT (cast__1_) AS cast1,
COUNT (cast__2_) AS cast2,
COUNT (cast__3_) AS cast3,
COUNT (cast__4_) AS cast4,
FROM `dataproject1-351413.movie_data.movies` AS movies
WHERE
cast__1_ IS NOT Null
GROUP BY
cast__1_
)
FROM `dataproject1-351413.movie_data.movies`
GROUP BY
cast__1_
(The intended result was two columns, pairing each actor with the number of films across the dataset, in case that is not clear from the query)

Answer 1

The structure of your query seems a bit skewed, you need to treat the aggregate query as a derived table, such as:
SELECT cast__1_, cast1 + cast2 + cast3 + cast4 AS num_films
from (
SELECT
cast__1_,
COUNT (cast__1_) AS cast1,
COUNT (cast__2_) AS cast2,
COUNT (cast__3_) AS cast3,
COUNT (cast__4_) AS cast4,
FROM `dataproject1-351413`.movie_data.movies
WHERE cast__1_ IS NOT Null
GROUP BY cast__1_
)t;