Inserting data from one BigQuery table to another returns 0 rows on group by - sql

Question

I am trying to do insert data from one BigQuery table to another by running the query shown below but I get 0 rows in return. However if I take out the Survey column, I get the correct number of rows in return.
Both the nested fields have the same type of schema. I have checked and double checked the column names too but can´t seem to figure out what´s wrong with Survey field.
INSERT INTO destination_table
(
Title, Description, Address, Survey
)
SELECT
Title as Title,
Description as Description,
[STRUCT(
ARRAY_AGG(STRUCT(Address_Instance.Field1, Address_Instance.Field2)) AS Address_Record
)]
as Address,
[STRUCT(
ARRAY_AGG(STRUCT(Survey_Instance.Field1, Survey_Instance.Field2)) AS Survey_Record
)]
as Survey
FROM
source_table,
UNNEST(Survey) AS Survey,
UNNEST(Survey_Instance) as Survey_Instance,
GROUP BY
Title,
Description
Here´s how the schema of my source table looks like:
[
{
"name": "Title",
"type": "STRING"
},
{
"name": "Description",
"type": "STRING"
},
{
"name": "Address",
"type": "RECORD",
"mode": "REPEATED",
"fields": [
{
"name": "Address_Instance",
"type": "RECORD",
"mode": "REPEATED",
"fields": [
{
"name": "Field1",
"type": "STRING"
},
{
"name": "Field2",
"type": "STRING"
}
]
}
]
},
{
"name": "Survey",
"type": "RECORD",
"mode": "REPEATED",
"fields": [
{
"name": "Survey_Instance",
"type": "RECORD",
"mode": "REPEATED",
"fields": [
{
"name": "Field1",
"type": "STRING"
},
{
"name": "Field2",
"type": "STRING"
}
]
}
]
},
]
While mapping to the destination table, I rename the nested repeated records but that´s not causing any problems. I am wondering if I am overlooking something important and need some suggestions and advice. Basically an extra set of eyes to help me figure what I am doing wrong.
Would appreciate some help. Thanks in advance.

Answer 1

Use explicit JOINs in general. In this case, use LEFT JOIN:
FROM source_table st LEFT JOIN
UNNEST(st.Survey) Survey
ON 1=1 LEFT JOIN
UNNEST(Survey.Survey_Instance) Survey_Instance
ON 1=1