JSON to SQL - Extracting from JSON Array? - sql

Question

I have an exercise to extract some data from a larger JSON object however the data is added as multiple objects or perhaps an array of sorts.
An example below;
DECLARE #json NVARCHAR(MAX) = '{
"N.data.-ce731645-e4ef-4784-bc02-bb90b4c9e9e6": "Some Data",
"N.data.sessionDates-7f1790d3-9175-43aa-962b-161ee3b8615f": [
{
"date_1": "2018-10-20T23:00:00.000Z"
},
{
"date_1": "2018-10-21T23:00:00.000Z"
}
]
}'
I need to extract these datetime entries from the "date_1" identifier into ideally a CSV list. From that I can do my own manipulations.
2018-10-20T23:00:00.000Z, 2018-10-21T23:00:00.000Z
I am familiar with JSON_VALUE() however not with its use outside of a simple piece of one dimensional data.
What I have so far;
DECLARE #json NVARCHAR(MAX) = '{
"N.data.-ce731645-e4ef-4784-bc02-bb90b4c9e9e6": "Some Data",
"N.data.sessionDates-7f1790d3-9175-43aa-962b-161ee3b8615f": [
{
"date_1": "2018-10-20T23:00:00.000Z"
},
{
"date_1": "2018-10-21T23:00:00.000Z"
}
]
}'
SELECT value FROM OPENJSON(#json)
Is there a way to achive the expected output outside of complex substring() and replace() uses?
Using SQL Server 2017
Microsoft SQL Server 2017 (RTM) - 14.0.1000.169 (X64) Aug 22 2017 17:04:49 Copyright (C) 2017 Microsoft Corporation Express Edition (64-bit) on Windows Server 2012 R2 Datacenter 6.3 <X64> (Build 9600: ) (Hypervisor)
Thanks

Answer 1

Since SQL Server 2017, the extraction can be done via native OPENJSON:
DECLARE #json NVARCHAR(MAX) = '{
"N.data.sessionDates-7f1790d3-9175-43aa-962b-161ee3b8615f": [
{
"date_1": "2018-10-20T23:00:00.000Z"
},
{
"date_1": "2018-10-21T23:00:00.000Z"
}
]
}'
SELECT
JSON_VALUE(child_value.value, '$.date_1') AS [key]
FROM OPENJSON(#json, '$') AS nda
cross apply openjson(nda.value, '$') as child_value
Results to:
key
2018-10-20T23:00:00.000Z
2018-10-21T23:00:00.000Z
Is there a way to adjust this to extract the values for a specific
key, "N.data.sessionDates-7f1790d3-9175-43aa-962b-161ee3b8615f" in the
example
In this case, that query can be slightly simplified to:
DECLARE #id nvarchar(200) = 'N.data.sessionDates-7f1790d3-9175-43aa-962b-161ee3b8615f'
SELECT
JSON_VALUE(nda.value, '$.date_1') AS [key]
FROM OPENJSON(#json, concat('$."',#id,'"')) AS nda
or without parametrization:
SELECT
JSON_VALUE(nda.value, '$.date_1') AS [key]
FROM OPENJSON(#json, '$."N.data.sessionDates-7f1790d3-9175-43aa-962b-161ee3b8615f"') AS nda

Answer 2

Use a cross apply with OPENJSON() using a with_clause:
DECLARE #json NVARCHAR(MAX) = '{
"N.data.sessionDates-7f1790d3-9175-43aa-962b-161ee3b8615f": [
{
"date_1": "2018-10-20T23:00:00.000Z"
},
{
"date_1": "2018-10-21T23:00:00.000Z"
}
]
}';
SELECT [b].*
FROM OPENJSON(#json) [a]
CROSS APPLY
OPENJSON([a].[Value])
WITH (
[date_1] DATETIME '$.date_1'
) [b];

Answer 3

Another possible approach, using OPENJSON(). With this approach you can get key/value pairs from your nested JSON array, even if this array has different key names.
DECLARE #json nvarchar(max)
SET #json =
N'{"N.data.sessionDates-7f1790d3-9175-43aa-962b-161ee3b8615f": [
{
"date_1": "2018-10-20T23:00:00.000Z"
},
{
"date_1": "2018-10-21T23:00:00.000Z"
},
{
"date_2": "2019-10-21T23:00:00.000Z"
}
]
}'
SELECT
x.[key] AS SessionData,
z.[key],
z.[value]
FROM OPENJSON(#json) x
CROSS APPLY (SELECT * FROM OPENJSON(x.[value])) y
CROSS APPLY (SELECT * FROM OPENJSON(y.[value])) z
--WHERE z.[key] = 'date_1'
Output:
SessionData key value
N.data.sessionDates-7f1790d3-9175-43aa-962b-161ee3b8615f date_1 2018-10-20T23:00:00.000Z
N.data.sessionDates-7f1790d3-9175-43aa-962b-161ee3b8615f date_1 2018-10-21T23:00:00.000Z
N.data.sessionDates-7f1790d3-9175-43aa-962b-161ee3b8615f date_2 2019-10-21T23:00:00.000Z
Update:
If you want to filter by key name, next may help:
DECLARE #json NVARCHAR(MAX) = '{
"N.data.-ce731645-e4ef-4784-bc02-bb90b4c9e9e6": "Some Data",
"N.data.sessionDates-7f1790d3-9175-43aa-962b-161ee3b8615f": [
{
"date_1": "2018-10-20T23:00:00.000Z"
},
{
"date_1": "2018-10-21T23:00:00.000Z"
}
]
}'
SELECT z.[value]
--SELECT STRING_AGG(z.[value], ', ') [Data] -- with string aggregation
FROM OPENJSON(#json) x
CROSS APPLY (SELECT * FROM OPENJSON(x.[value])) y
CROSS APPLY (SELECT * FROM OPENJSON(y.[value])) z
WHERE x.[key] = 'N.data.sessionDates-7f1790d3-9175-43aa-962b-161ee3b8615f'
Output:
value
2018-10-20T23:00:00.000Z
2018-10-21T23:00:00.000Z
-- With string aggregation
--Data
--2018-10-20T23:00:00.000Z, 2018-10-21T23:00:00.000Z