DECLARE @js nvarchar(max) =N'{
    "address": {
                "state": "Example State",
                "street": "Example St",
                "number": "4/33",
                "suburb": "Example Suburb",
                "postcode": "0000",
                "country": "Example Country"
    }
}'

SELECT
    [State]
    ,[Number]
    ,CASE
        WHEN CHARINDEX('/', [Number]) IS NOT NULL
        THEN SUBSTRING([Number], 0, CHARINDEX('/', [Number]))
        ELSE NULL
    END AS unit_number
    ,CASE
        WHEN CHARINDEX('/', [Number]) IS NOT NULL
        THEN SUBSTRING([Number], CHARINDEX('/', [Number])+1, LEN([Number]))
        ELSE [Number]
    END AS street_number
FROM
    OPENJSON(@js)
    WITH (
        [State] NVARCHAR(200) '$.address.state'
        ,[Number] NVARCHAR(200) '$.address.number'
    )