converting NULLs to 0 in an ARRAY join - sql

Question

I have an table that has nulls and I want to replace them with 0s. The table was generated by a join between a table ('Table_A') and an array ('Table_B).
Current table:
Date | Sessions | ID | City
------+----------+-------------+-------------
06-02 | 1 | 107 | Cardiff
| | 102 | Paris
06-03 | NULL | NULL | NULL
11-12 | 1 | 105 | Amsterdam
| | 107 | Cardiff
| | 103 | Rome
27-06 | NULL | NULL | NULL
Desirable Output:
Date | Sessions | ID | City
------+----------+-------------+-------------
06-02 | 1 | 107 | Cardiff
| | 102 | Paris
06-03 | 0 | 0 | 0
11-12 | 1 | 105 | Amsterdam
| | 107 | Cardiff
| | 103 | Rome
27-06 | 0 | 0 | 0
Below is my current code. I can't remove the 'ignore nulls' because it wouldn't allow me to do the join.
select date, Sessions,
array_agg(a.ID ignore nulls) as ID, array_agg(City ignore nulls) as City
from Table_B b, unnest (ID) as ID_un
left join Table_A a on ID_un = cast(a.ID as string)
group by 1, 2
...

Answer 1

Current Table
WITH sample_data AS (
SELECT '06-02' Date, 1 Sessions, [107, 102] ID, ['Cardiff', 'Paris'] City UNION ALL
SELECT '06-03', NULL, [], [] UNION ALL
SELECT '11-12', 1, [105, 107, 103], ['Amsterdam', 'Cardiff', 'Rome'] UNION ALL
SELECT '27-06', NULL, NULL, NULL
)
Note that an empty array is displayed as null in the output.
Desired Output
I have an table that has nulls and I want to replace them with 0s.
Below query replaces an empty or null array to [0] or ['0'] depending on it's type.
SELECT Date,
COALESCE(Sessions, 0) AS Sessions,
IF(ARRAY_LENGTH(ID) = 0 OR ID IS NULL, [0], ID) AS ID,
IF(ARRAY_LENGTH(City) = 0 OR City IS NULL, ['0'], City) AS City,
-- below is a little bit concise notation of above two.
-- IF(ARRAY_LENGTH(ID) > 0, ID, [0]) AS ID,
-- IF(ARRAY_LENGTH(City) > 0, City, ['0']) AS City,
FROM sample_data;
■ Query results