Format SQL output to custom JSON - sql

Question

I have this table which is very simple with this data
CREATE TABLE #Prices
(
ProductId int,
SizeId int,
Price int,
Date date
)
INSERT INTO #Prices
VALUES (1, 1, 100, '2020-01-01'),
(1, 1, 120, '2020-02-01'),
(1, 1, 130, '2020-03-01'),
(1, 2, 100, '2020-01-01'),
(1, 2, 100, '2020-02-01'),
(2, 1, 100, '2020-01-01'),
(2, 1, 120, '2020-02-01'),
(2, 1, 130, '2020-03-01'),
(2, 2, 100, '2020-01-01'),
(2, 2, 100, '2020-02-01')
I would like to format the output to be something like this:
{
"Products": [
{
"Product": 2,
"UnitSizes": [
{
"SizeId": 1,
"PerDate": [
{
"Date": "2020-01-02",
"Price": 870.0
},
{
"Date": "2021-04-29",
"Price": 900.0
}
]
},
{
"SizeId": 2,
"PerDate": [
{
"Date": "2020-01-02",
"Price": 435.0
},
{
"Date": "2021-04-29",
"Price": 450.0
}
]
}
]
},
{
"Product": 4,
"UnitSizes": [
{
"SizeId": 1,
"PerDate": [
{
"Date": "2020-01-02",
"Price": 900.0
}
]
}
]
}
]
}
I almost have it but I don't know how to format to get the array inside 'PerDate'. This is what I have
SELECT
ProductId AS [Product],
SizeId AS 'Sizes.SizeId',
date AS 'Sizes.PerDate.Date',
price AS 'Sizes.PerDate.Price'
FROM
#Prices
ORDER BY
ProductId, [Sizes.SizeId], Date
FOR JSON PATH, ROOT('Products')
I have tried with FOR JSON AUTO and nothing, I've tried with JSON_QUERY() but I was not able to achieve the result I want.
Every help will be very appreciated.
Thanks

Answer 1

Unfortunately, SQL Server does not have the JSON_AGG function, which means you would normally need to use a number of correlated subqueries and keep on rescanning the base table.
However, we can simulate it by using STRING_AGG against single JSON objects generated in an APPLY. This means that we only scan the base table once.
Use of JSON_QUERY with no path prevents double-escaping
WITH PerDate AS (
SELECT
p.ProductId,
p.SizeId,
PerDate = '[' + STRING_AGG(j.PerDate, ',') WITHIN GROUP (ORDER BY p.Date) + ']'
FROM #Prices AS p
CROSS APPLY ( -- This produces multiple rows of single JSON objects
SELECT p.Date, p.Price
FOR JSON PATH, WITHOUT_ARRAY_WRAPPER
) j(PerDate)
GROUP BY
p.ProductId,
p.SizeId
),
UnitSizes AS (
SELECT
p.ProductId,
UnitSizes = '[' + STRING_AGG(j.UnitSizes, ',') WITHIN GROUP (ORDER BY p.SizeId) + ']'
FROM PerDate p
CROSS APPLY (
SELECT p.SizeId, PerDate = JSON_QUERY(p.PerDate)
FOR JSON PATH, WITHOUT_ARRAY_WRAPPER
) j(UnitSizes)
GROUP BY
p.ProductId
)
SELECT
Product = p.ProductId,
UnitSizes = JSON_QUERY(p.UnitSizes)
FROM UnitSizes p
ORDER BY p.ProductId
FOR JSON PATH, ROOT('Products');
db<>fiddle

Answer 2

This is one way of doing it
DROP TABLE IF EXISTS #Prices
CREATE TABLE #Prices
(
ProductId INT,
SizeId INT,
Price INT,
Date DATE
)
-- SQL Prompt formatting off
INSERT INTO #Prices
VALUES (1, 1, 100, '2020-01-01'),
(1, 1, 120, '2020-02-01'),
(1, 1, 130, '2020-03-01'),
(1, 2, 100, '2020-01-01'),
(1, 2, 100, '2020-02-01'),
(2, 1, 100, '2020-01-01'),
(2, 1, 120, '2020-02-01'),
(2, 1, 130, '2020-03-01'),
(2, 2, 100, '2020-01-01'),
(2, 2, 100, '2020-02-01')
-- SQL Prompt formatting on
SELECT m.ProductId AS Product,
(
SELECT s.SizeId,
(
SELECT p.Date,
p.Price
FROM #Prices AS p
WHERE p.SizeId = s.SizeId
GROUP BY p.Date,
p.Price
ORDER BY p.Date
FOR JSON PATH
) AS PerDate
FROM #Prices AS s
WHERE s.ProductId = m.ProductId
GROUP BY s.SizeId
ORDER BY s.SizeId
FOR JSON PATH
) AS UnitSizes
FROM #Prices AS m
GROUP BY m.ProductId
ORDER BY m.ProductId
FOR JSON PATH, ROOT('Products')
Output:
{
"Products":
[
{
"Product": 1,
"UnitSizes":
[
{
"SizeId": 1,
"PerDate":
[
{
"Date": "2020-01-01",
"Price": 100
},
{
"Date": "2020-02-01",
"Price": 120
},
{
"Date": "2020-03-01",
"Price": 130
}
]
},
{
"SizeId": 2,
"PerDate":
[
{
"Date": "2020-01-01",
"Price": 100
},
{
"Date": "2020-02-01",
"Price": 100
}
]
}
]
},
{
"Product": 2,
"UnitSizes":
[
{
"SizeId": 1,
"PerDate":
[
{
"Date": "2020-01-01",
"Price": 100
},
{
"Date": "2020-02-01",
"Price": 120
},
{
"Date": "2020-03-01",
"Price": 130
}
]
},
{
"SizeId": 2,
"PerDate":
[
{
"Date": "2020-01-01",
"Price": 100
},
{
"Date": "2020-02-01",
"Price": 100
}
]
}
]
}
]
}