The usefulness of ->> operator is indisputable, but even with boolean or numeric values, with good binary internal representation, it returns JSONB value as text data type.
The simple *(myJSONB->>'myField')::expectedType* is not enough because: 1) there are no internal optimization, need two-step casting, first bynary-to-text, them text-to-expectedType. 2) if expectedType is not the expected (in the associated jsonb_typeof), generates an error... The ideal "return NULL" convention is not easy to implement with usual casting. More details and some examples at http://stackoverflow.com/q/34579758/287948 - - - - CONTEXT OF USEFULNESS As section "8.14. JSON Types" in the pg9.4 guide, "Representing data as JSON can be considerably more flexible (...) is quite possible for both approaches to co-exist and complement each other (...) However, even for applications where maximal flexibility is desired, it is still recommended that JSON documents have a somewhat fixed structure". The proposed casting functions of JSONB is a part of "predictable but fluid structure" demands in JSON representation, and makes it easier to write queries that mix usual data types with JSONB. - - - - Formal requeriment <https://en.wikipedia.org/wiki/Requirements_analysis> for a C implementation below CREATE FUNCTION jbval_to_numeric(JSONB, varchar) RETURNS numeric AS $f$ SELECT CASE WHEN jsonb_typeof($1->$2)='number' THEN ($1->>$2)::numeric ELSE NULL::numeric END;$f$ LANGUAGE sql IMMUTABLE; CREATE FUNCTION jbval_to_float(JSONB, varchar) RETURNS float AS $f$ SELECT CASE WHEN jsonb_typeof($1->$2)='number' THEN ($1->>$2)::float ELSE NULL::float END;$f$ LANGUAGE sql IMMUTABLE; CREATE FUNCTION jbval_to_int(JSONB, varchar, boolean DEFAULT true) RETURNS int AS $f$ SELECT CASE WHEN jsonb_typeof($1->$2)='number' THEN CASE WHEN $3 THEN ($1->>$2)::int ELSE ($1->>$2)::float::int END ELSE NULL::int END;$f$ LANGUAGE sql IMMUTABLE; CREATE FUNCTION jbval_to_boolean(JSONB, varchar) RETURNS boolean AS $f$ SELECT CASE WHEN jsonb_typeof($1->$2)='boolean' THEN ($1->>$2)::boolean ELSE NULL::boolean END;$f$ LANGUAGE sql IMMUTABLE;
