Decode Base64 using a column as a variable - sql

Question

Objective:
I would like to Decode a Base64 column from a table using the OPENJSON function and extract the 'a' key from that decoded string as such:
DECLARE #JSON nvarchar(MAX) = 'column name' -- Here i am puting 'column name' because im not sure how to insert a column into a declared variable.
SELECT [Value]
FROM OPENJSON(#JSON)
WHERE [key] = 'a';
Situation:
I have a column ('ProductsBase64') that is Base64 encoded that I would like to decode.
Example of a unique string:
I would like to decode an entire column however
DECLARE #JSON nvarchar(MAX) = N'{"a":1,"b":2,"c":3,"d":4}';
SELECT *
FROM OPENJSON(#JSON)
where type = 2
Results:
key value type
a 1 2
b 2 2
c 3 2
d 4 2

Answer 1

Assuming the original text encoding is compatible with varchar you can use the below (uses XML xs:base64Binary method to do the base 64 decoding, that is then cast to VARCHAR and finally passed as input to OPENJSON)
CREATE TABLE #t
(
ProductsBase64 VARCHAR(max)
)
INSERT INTO #t
VALUES ('eyJhIjoxLCJiIjoyLCJjIjozLCJkIjo0fQ=='); /*{"a":1,"b":2,"c":3,"d":4} */
SELECT ca.*
FROM #t
CROSS APPLY (SELECT *
FROM OPENJSON(
CONVERT (
VARCHAR(MAX),
CAST('' AS XML).value('xs:base64Binary(sql:column("ProductsBase64"))', 'VARBINARY(MAX)')
)
)
WHERE type = 2) ca