Why same query results are different on BigQuery editor and sqlalchemy? - google-bigquery

Question

My bigquery query is :
SELECT d.type AS `error_type`, count('d.type') AS `count`
FROM `table_android`, unnest(`table_android`.`exceptions`) AS `d`
WHERE `table_android`.`event_timestamp` BETWEEN '2022-12-15' AND '2022-12-20' GROUP BY `error_type` ORDER BY `count` desc;
This query is working fine in bigquery editor. But same version of query with sqlalchemy I could not get same results.
sqlalchemy query :
sa.select(
sa.literal_column("d.type").label("Error_Type"),
sa.func.count("Error_Type").label("count"),
)
.select_from(sa.func.unnest(table_android.c.exceptions).alias("d"))
.group_by("Error_Type")
.order_by(desc("count"))
.where(table_android.c.event_timestamp.between('2022-12-15', '2022-12-20'))
.cte("main_table")
Correct result :
Wrong result:
I am using python-bigquery-sqlalchemy library. table_android.exceptions column struct is like that :
column types :
And this is render of sqlalchemy query :
SELECT `d`.`type` AS `Error_Type`, count(`d`.`type`) AS `count` FROM `table_android`, unnest(`table_android`.`exceptions`) AS `d` WHERE `table_android`.`event_timestamp` BETWEEN '2022-12-05' AND '2022-12-20' GROUP BY `Error_Type` ORDER BY `count` DESC
I see correct result in bigquery editor. But sqlalchemy is not shows correct result. How should i edit my sqlalchemy query for correct results ?

Answer 1

I don't have bigquery so I can't test this but I think you want column and not literal_column. Also I think you can create an implicit CROSS JOIN by including both the table and the unnested column in the select_from.
# I'm testing with postgresql but it doesn't have easy to make structs
from sqlalchemy.dialects import postgresql
table_android = Table("table_android", metadata,
Column("id", Integer, primary_key=True),
Column("exceptions", postgresql.ARRAY(String)),
Column("event_timestamp", Date))
from sqlalchemy.sql import column, func, select
d = func.unnest(table_android.c.exceptions).alias("d")
# You might be able to do d.column["type"].label("Error_Type")
type_col = column("d.type").label("Error_Type")
count_col = func.count(type_col).label("count")
print (select(
type_col,
count_col,
)
.select_from(table_android, d)
.group_by(type_col)
.order_by(count_col)
.where(table_android.c.event_timestamp.between('2022-12-15', '2022-12-20'))
.cte("main_table"))