How to extract a value in a JSON table on BigQuery? - sql

Question

I have a JSON table which has over 30.000 rows. There are different rows like this:
JSON_columns
------------
{
"level": 20,
"nickname": "ABCDE",
"mission_name": "take_out_the_trash",
"mission_day": "150",
"duration": "0",
"properties": []
}
{
"nickname": "KLMNP",
"mission_name": "recycle",
"mission_day": "180",
"properties": [{
"key": "bottle",
"value": {
"string_value": "blue_bottle"
}
}, {
"key": "bottleRecycle",
"value": {
"string_value": "true"
}
}, {
"key": "price",
"value": {
"float_value": 21.99
}
}, {
"key": "cost",
"value": {
"float_value": 15.39
}
}]
}
I want to take the sum of costs the table. But firtsly, I want to extract the cost from the table.
I tried the code below. It returns null:
SELECT JSON_VALUE('$.properties[3].value.float_value') AS profit
FROM `missions.missions_study`
WHERE mission_name = "recycle"
My question is, how can I extract the cost values right, and sum them?

Answer 1

Common way to extract cost from your json is like below.
WITH sample_table AS (
SELECT '{"level":20,"nickname":"ABCDE","mission_name":"take_out_the_trash","mission_day":"150","duration":"0","properties":[]}' json
UNION ALL
SELECT '{"nickname":"KLMNP","mission_name":"recycle","mission_day":"180","properties":[{"key":"bottle","value":{"string_value":"blue_bottle"}},{"key":"bottleRecycle","value":{"string_value":"true"}},{"key":"price","value":{"float_value":21.99}},{"key":"cost","value":{"float_value":15.39}}]}' json
)
SELECT SUM(cost) AS total FROM (
SELECT CAST(JSON_VALUE(prop, '$.value.float_value') AS FLOAT64) AS cost
FROM sample_table, UNNEST(JSON_QUERY_ARRAY(json, '$.properties')) prop
WHERE JSON_VALUE(json, '$.mission_name') = 'recycle'
AND JSON_VALUE(prop, '$.key') = 'cost'
);