PostgreSQL - Add key to each objects of an JSONB array

Question

My database contains a table which has a column with jsonb type, and I want to update a part of these data using functions/operators from postgreSQL

Answer 1

The approach with jsonb_array_elements and jsonb_set was the right idea, but somehow you nested them the wrong way round:

UPDATE myTable SET myColumn = jsonb_set(myColumn, '{A}', (
  SELECT jsonb_agg( element || '{"myArray":[]}' )
  FROM jsonb_array_elements(myColumn -> 'A') element
));

^{(online demo)}

Btw if your column already has jsonb data type, you shouldn't need any casts.