Oracle 21c

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SELECT json_object(
         'a' value 'blah' FORMAT JSON,
         'b' value 'blah' FORMAT JSON,
         'c' value 'blah' FORMAT JSON
       ) AS formatted_values
FROM   DUAL


FORMATTED_VALUES


{"a":blah,"b":blah,"c":blah}


SELECT json_object(
         'a' value 'blah',
         'b' value 'blah',
         'c' value 'blah' FORMAT JSON
       ) AS formatted_values
FROM   DUAL


FORMATTED_VALUES


{"a":"blah","b":"blah","c":blah}


SELECT json_object(
         'a' value 'blah',
         'b' value 'blah',
         'c' value 'blah'
       ) AS formatted_values
FROM   DUAL


FORMATTED_VALUES


{"a":"blah","b":"blah","c":"blah"}


SELECT json_object(
         'a' value '"blah"' FORMAT JSON,
         'b' value '"blah"' FORMAT JSON,
         'c' value '"blah"' FORMAT JSON
       ) AS formatted_values
FROM   DUAL


FORMATTED_VALUES


{"a":"blah","b":"blah","c":"blah"}