Postgres 17

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select to_json(1);

to_json

1

SELECT 1

SELECT 
  to_json(NULL::text) ;

to_json

null

SELECT 1

SELECT 
  pg_typeof(NULL::text) ;

pg_typeof

text

SELECT 1

SELECT 
  pg_typeof(to_json(NULL::text)) ;

pg_typeof

json

SELECT 1

select 'null'::jsonb is null;

?column?

f

SELECT 1

select 'null'::json is null;

?column?

f

SELECT 1

SELECT 
  to_json(NULL::text)  is null;

?column?

t

SELECT 1