How to generate a JSON value array in Azure SQL - json

Question

DECLARE #segArr NVARCHAR(max)
set #segArr = N'[1,2,3]'
DECLARE #segTb table (
k int,
v NVARCHAR(20)
);
insert into #segTb
VALUES
(0, 'a'),
(1, 'b'),
(2, 'c'),
(3, 'd'),
(4, 'e'),
(5, 'f');
select t.v from #segTb t
JOIN openjson(#segArr) a on a.[key] = t.k
for JSON auto;
I have a simple table with a key-value like structure and a JSON array that is a list of keys of the values I wanted.
The select statement can create the desired result, but the JSON format is wrong. It outputs an array of objects.
[
{
"v": "a"
},
{
"v": "b"
},
{
"v": "c"
}
]
But what I needed is an array of direct values.
[ "a", "b", "c" ]

Answer 1

You can use more conventional string manipulation methods to create JSON arrays in Azure SQL DB such as STRING_AGG which aggregates strings with the given separator (eg comma) and QUOTENAME which surrounds strings with the given quote character. A simple example:
SELECT QUOTENAME( STRING_AGG( QUOTENAME(v, '"' ), ',' ), '[' ) AS yourArray
FROM
(
SELECT t.v FROM #segTb t
INNER JOIN OPENJSON(#segArr) a ON a.[key] = t.k
) x;
For your particular example you could just create a user-defined table-type, with CREATE TYPE. This would have the advantage of you being able to add a primary key to the type, to guarantee duplicates cannot be added, give the optimizer a bit more info at run-time and use native relational abilities rather than bolted-on NOSQL abilities. A simple example which should run end-to-end:
IF NOT EXISTS ( SELECT * FROM sys.types st INNER JOIN sys.schemas ss ON st.schema_id = ss.schema_id WHERE st.name = N'tvpItems' AND ss.name = N'dbo')
CREATE TYPE dbo.tvpItems AS TABLE
(
k INT PRIMARY KEY
);
GO
DECLARE #items AS dbo.tvpItems
INSERT INTO #items VALUES ( 1 ), ( 2 ), ( 3 )
DECLARE #segTb TABLE (
k INT,
v NVARCHAR(20)
);
INSERT INTO #segTb
VALUES
(0, 'a'),
(1, 'b'),
(2, 'c'),
(3, 'd'),
(4, 'e'),
(5, 'f');
SELECT t.v
FROM #segTb t
INNER JOIN #items i ON i.k = t.k
FOR JSON AUTO;