What JSON format does STRIP_OUTER_ARRAY support? - json

Question

I have a file composed of a single array containing multiple records.
{
"Client": [
{
"ClientNo": 1,
"ClientName": "Alpha",
"ClientBusiness": [
{
"BusinessNo": 1,
"IndustryCode": "12345"
},
{
"BusinessNo": 2,
"IndustryCode": "23456"
}
]
},
{
"ClientNo": 2,
"ClientName": "Bravo",
"ClientBusiness": [
{
"BusinessNo": 1,
"IndustryCode": "34567"
},
{
"BusinessNo": 2,
"IndustryCode": "45678"
}
]
}
]
}
I load it with the following code:
create or replace stage stage.test
url='azure://xxx/xxx'
credentials=(azure_sas_token='xxx');
create table if not exists stage.client (json_data variant not null);
copy into stage.client_test
from #stage.test/client_test.json
file_format = (type = 'JSON' strip_outer_array = true);
Snowflake imports the entire file as one row.
I would like the the COPY INTO command to remove the outer array structure and load the records into separate table rows.
When I load larger files, I hit the size limit for variant and get the error Error parsing JSON: document is too large, max size 16777216 bytes.

Answer 1

If you can import the file into Snowflake, into a single row, then you can use LATERAL FLATTEN on the Clients field to generate one row per element in the array.
Here's a blog post on LATERAL and FLATTEN (or you could look them up in the snowflake docs):
https://support.snowflake.net/s/article/How-To-Lateral-Join-Tutorial
If the format of the file is, as specified, a single object with a single property that contains an array with 500 MB worth of elements in it, then perhaps importing it will still work -- if that works, then LATERAL FLATTEN is exactly what you want. But that form is not particularly great for data processing. You might want to use some text processing script to massage the data if that's needed.

Answer 2

RECOMMENDATION #1:
The problem with your JSON is that it doesn't have an outer array. It has a single outer object containing a property with an inner array.
If you can fix the JSON, that would be the best solution, and then STRIP_OUTER_ARRAY will work as you expected.
You could also try to recompose the JSON (an ugly business) after reading line for line with:
CREATE OR REPLACE TABLE X (CLIENT VARCHAR);
COPY INTO X FROM (SELECT $1 CLIENT FROM #My_Stage/Client.json);
User Response to Recommendation #1:
Thank you. So from what I gather, COPY with STRIP_OUTER_ARRAY can handle a file starting and ending with square brackets, and parse the file as if they were not there.
The real files don't have line breaks, so I can't read the file line by line. I will see if the source system can change the export.
RECOMMENDATION #2:
Also if you would like to see what the JSON parser does, you can experiment using this code, I have parsed JSON on the copy command using similar code. Working with your JSON data in small project can help you shape the Copy command to work as intended.
CREATE OR REPLACE TABLE SAMPLE_JSON
(ID INTEGER,
DATA VARIANT
);
INSERT INTO SAMPLE_JSON(ID,DATA)
SELECT
1,parse_json('{
"Client": [
{
"ClientNo": 1,
"ClientName": "Alpha",
"ClientBusiness": [
{
"BusinessNo": 1,
"IndustryCode": "12345"
},
{
"BusinessNo": 2,
"IndustryCode": "23456"
}
]
},
{
"ClientNo": 2,
"ClientName": "Bravo",
"ClientBusiness": [
{
"BusinessNo": 1,
"IndustryCode": "34567"
},
{
"BusinessNo": 2,
"IndustryCode": "45678"
}
]
}
]
}');
SELECT
C.value:ClientNo AS ClientNo
,C.value:ClientName::STRING AS ClientName
,ClientBusiness.value:BusinessNo::Integer AS BusinessNo
,ClientBusiness.value:IndustryCode::Integer AS IndustryCode
from SAMPLE_JSON f
,table(flatten( f.DATA,'Client' )) C
,table(flatten(c.value:ClientBusiness,'')) ClientBusiness;
User Response to Recommendation #2:
Thank you for the parse_json example!
Trouble is, the real files are sometimes 500 MB, so the parse_json function chokes.
Follow-up on Recommendation #2:
The JSON needs to be in the NDJSON http://ndjson.org/ format. Otherwise the JSON will be impossible to parse because of the potential for large files.
Hope the above helps other running into similar questions!