Oracle 18c

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select JSON_VALUE('{"-": "hello", "de":"hallo"}','$."de"') from DUAL

JSON_VALUE('{"-":"HELLO","DE":"HALLO"}','$."DE"')

hallo

select JSON_VALUE('{"-": "hello", "de":"hallo"}','$."-"') from DUAL

JSON_VALUE('{"-":"HELLO","DE":"HALLO"}','$."-"')

hello

-- In 12c, the equivalent of this error is ORA-40442 
select JSON_VALUE('{"-": "hello", "de":"hallo"}','$.-') from DUAL
ORA-40597: JSON path expression syntax error ('$.-')
JZN-00217: Key step contains unexpected characters
at position 3

-- In 12c, the equivalent of this error is ORA-40442 
select JSON_VALUE('{"-": "hello", "de":"hallo"}','$.d-e') from DUAL
ORA-40597: JSON path expression syntax error ('$.d-e')
JZN-00201: Unquoted punctuation in step
at position 5

select JSON_VALUE('{"-": "hello", "de":"hallo"}','$.de') from DUAL

JSON_VALUE('{"-":"HELLO","DE":"HALLO"}','$.DE')

hallo