Read in nested JSON file in SQL Server - json

Question

I am trying to read the following information taken from a nested json file in SQL Server:
Declare #json nvarchar(max)
SELECT #json =
N'{
"Energy":
{
"Energy-X/A": [
[
100.123456, null
],
[
101.123456, null
]
],
"Energy-X/B": [
[
102.123456, null
],
[
103.123456, null
]
]
}
}'
select
JSON_VALUE(a.value, '$.energy.Energy-X/A') as [Energy-X/A],
JSON_VALUE(b.value, '$.energy.Energy-X/B') as [Energy-X/B]
from OPENJSON(#json, '$.Energy') as a
CROSS APPLY OPENJSON(a.value, '$.energy') as b
The expected output should be that there are two columns with two entries for each row:
Energy-X/A
100.123456, null
101.123456, null
Energy-X/B
102.123456, null
103.123456, null
However, I am encountering two problems which I could not figure out:
If I execute the SQL statement nothing happens which indicates that I am obviously doing something wrong.
I have almost 1000 entries like "Energy-X/A", "Energy-X/B", "Energy-X/AC", etc.. Is there any better approach to extract the information without reusing the "JSON_VALUE()" function and introducing, e.g., b. value?
I am grateful for any help!

Answer 1

SQL Server won't return the data quite like you're expecting. json_value() is used to return scalar values such as strings, numbers and booleans, but when you want to return an array (or array of arrays) or objects you can use json_query() to return a snippet of the JSON data. For example:
select
json_query(Energy, '$."Energy-X/A"') as [Energy-X/A],
json_query(Energy, '$."Energy-X/B"') as [Energy-X/B]
from openjson (#json) with (
Energy nvarchar(max) as json
) as a;
Returns the output:
Energy-X/A Energy-X/B
------------------------ ----------------------------
[ [
[ [
100.123456, null 102.123456, null
], ],
[ [
101.123456, null 103.123456, null
] ]
] ]
The query could be simplified to the following, which yields the same result:
select
json_query(#json, '$.Energy."Energy-X/A"') as [Energy-X/A],
json_query(#json, '$.Energy."Energy-X/B"') as [Energy-X/B];
Edit...
If the JSON snippets of Energy-X/A and Energy-X/B are not sufficient for your purpose then you need to know their structure and parse them manually.
If they will consistently be 2 element arrays of 2 element arrays and you want to produce a row for each outer array that contains a comma-delimited list of the inner array's elements you can use a query such as the following (note: this requires SQL Server 2017 or later to make use of the string_agg() function):
select
commaDelimited.*
from openjson (#json) with (
energyXA nvarchar(max) '$.Energy."Energy-X/A"' as json,
energyXB nvarchar(max) '$.Energy."Energy-X/B"' as json
) as energy
cross apply (
select
(select string_agg(isnull(value, 'null'), ',') from openjson(energyXA, '$[0]')),
(select string_agg(isnull(value, 'null'), ',') from openjson(energyXB, '$[0]'))
union all
select
(select string_agg(isnull(value, 'null'), ',') from openjson(energyXA, '$[1]')),
(select string_agg(isnull(value, 'null'), ',') from openjson(energyXB, '$[1]'))
) commaDelimited ([Energy-X/A], [Energy-X/B]);
Which produces the results...
Energy-X/A
Energy-X/B
100.123456,null
102.123456,null
101.123456,null
103.123456,null