More regression test cases for json/jsonb extraction operators.

Cover some cases I omitted before, such as null and empty-string
elements in the path array.  This exposes another inconsistency:
json_extract_path complains about empty path elements but
jsonb_extract_path does not.

src/test/regress/expected/json.out

@@ -674,6 +674,12 @@ select '{"a": [{"b": "c"}, {"b": "cc"}]}'::json -> 'z';
  
 (1 row)
 
+select '{"a": [{"b": "c"}, {"b": "cc"}]}'::json -> '';
+ ?column? 
+----------
+ 
+(1 row)
+
 select '[{"b": "c"}, {"b": "cc"}]'::json -> 1;
   ?column?   
 -------------
@@ -692,6 +698,50 @@ select '"foo"'::json -> 1;
 ERROR:  cannot extract element from a scalar
 select '"foo"'::json -> 'z';
 ERROR:  cannot extract element from a scalar
+select '{"a": [{"b": "c"}, {"b": "cc"}]}'::json ->> null::text;
+ ?column? 
+----------
+ 
+(1 row)
+
+select '{"a": [{"b": "c"}, {"b": "cc"}]}'::json ->> null::int;
+ ?column? 
+----------
+ 
+(1 row)
+
+select '{"a": [{"b": "c"}, {"b": "cc"}]}'::json ->> 1;
+ERROR:  cannot extract array element from a non-array
+select '{"a": [{"b": "c"}, {"b": "cc"}]}'::json ->> 'z';
+ ?column? 
+----------
+ 
+(1 row)
+
+select '{"a": [{"b": "c"}, {"b": "cc"}]}'::json ->> '';
+ ?column? 
+----------
+ 
+(1 row)
+
+select '[{"b": "c"}, {"b": "cc"}]'::json ->> 1;
+  ?column?   
+-------------
+ {"b": "cc"}
+(1 row)
+
+select '[{"b": "c"}, {"b": "cc"}]'::json ->> 3;
+ ?column? 
+----------
+ 
+(1 row)
+
+select '[{"b": "c"}, {"b": "cc"}]'::json ->> 'z';
+ERROR:  cannot extract field from a non-object
+select '"foo"'::json ->> 1;
+ERROR:  cannot extract element from a scalar
+select '"foo"'::json ->> 'z';
+ERROR:  cannot extract element from a scalar
 -- array length
 SELECT json_array_length('[1,2,3,{"f1":1,"f2":[5,6]},4]');
  json_array_length 
@@ -871,7 +921,7 @@ select '{"f2":["f3",1],"f4":{"f5":99,"f6":"stringy"}}'::json#>>array['f2','1'];
 (1 row)
 
 -- corner cases for same
-select '{"a": {"b":{"c": "foo"}}}'::json #> array[]::text[];
+select '{"a": {"b":{"c": "foo"}}}'::json #> '{}';
  ?column? 
 ----------
  
@@ -883,6 +933,10 @@ select '{"a": {"b":{"c": "foo"}}}'::json #> array['a'];
  {"b":{"c": "foo"}}
 (1 row)
 
+select '{"a": {"b":{"c": "foo"}}}'::json #> array['a', null];
+ERROR:  cannot call json_extract_path with null path elements
+select '{"a": {"b":{"c": "foo"}}}'::json #> array['a', ''];
+ERROR:  cannot call json_extract_path with empty path elements
 select '{"a": {"b":{"c": "foo"}}}'::json #> array['a','b'];
    ?column?   
 --------------
@@ -949,7 +1003,7 @@ select '42'::json #> array['0'];
  
 (1 row)
 
-select '{"a": {"b":{"c": "foo"}}}'::json #>> array[]::text[];
+select '{"a": {"b":{"c": "foo"}}}'::json #>> '{}';
  ?column? 
 ----------
  
@@ -961,6 +1015,10 @@ select '{"a": {"b":{"c": "foo"}}}'::json #>> array['a'];
  {"b":{"c": "foo"}}
 (1 row)
 
+select '{"a": {"b":{"c": "foo"}}}'::json #>> array['a', null];
+ERROR:  cannot call json_extract_path_text with null path elements
+select '{"a": {"b":{"c": "foo"}}}'::json #>> array['a', ''];
+ERROR:  cannot call json_extract_path_text with empty path elements
 select '{"a": {"b":{"c": "foo"}}}'::json #>> array['a','b'];
    ?column?   
 --------------

src/test/regress/expected/json_1.out

@@ -674,6 +674,12 @@ select '{"a": [{"b": "c"}, {"b": "cc"}]}'::json -> 'z';
  
 (1 row)
 
+select '{"a": [{"b": "c"}, {"b": "cc"}]}'::json -> '';
+ ?column? 
+----------
+ 
+(1 row)
+
 select '[{"b": "c"}, {"b": "cc"}]'::json -> 1;
   ?column?   
 -------------
@@ -692,6 +698,50 @@ select '"foo"'::json -> 1;
 ERROR:  cannot extract element from a scalar
 select '"foo"'::json -> 'z';
 ERROR:  cannot extract element from a scalar
+select '{"a": [{"b": "c"}, {"b": "cc"}]}'::json ->> null::text;
+ ?column? 
+----------
+ 
+(1 row)
+
+select '{"a": [{"b": "c"}, {"b": "cc"}]}'::json ->> null::int;
+ ?column? 
+----------
+ 
+(1 row)
+
+select '{"a": [{"b": "c"}, {"b": "cc"}]}'::json ->> 1;
+ERROR:  cannot extract array element from a non-array
+select '{"a": [{"b": "c"}, {"b": "cc"}]}'::json ->> 'z';
+ ?column? 
+----------
+ 
+(1 row)
+
+select '{"a": [{"b": "c"}, {"b": "cc"}]}'::json ->> '';
+ ?column? 
+----------
+ 
+(1 row)
+
+select '[{"b": "c"}, {"b": "cc"}]'::json ->> 1;
+  ?column?   
+-------------
+ {"b": "cc"}
+(1 row)
+
+select '[{"b": "c"}, {"b": "cc"}]'::json ->> 3;
+ ?column? 
+----------
+ 
+(1 row)
+
+select '[{"b": "c"}, {"b": "cc"}]'::json ->> 'z';
+ERROR:  cannot extract field from a non-object
+select '"foo"'::json ->> 1;
+ERROR:  cannot extract element from a scalar
+select '"foo"'::json ->> 'z';
+ERROR:  cannot extract element from a scalar
 -- array length
 SELECT json_array_length('[1,2,3,{"f1":1,"f2":[5,6]},4]');
  json_array_length 
@@ -871,7 +921,7 @@ select '{"f2":["f3",1],"f4":{"f5":99,"f6":"stringy"}}'::json#>>array['f2','1'];
 (1 row)
 
 -- corner cases for same
-select '{"a": {"b":{"c": "foo"}}}'::json #> array[]::text[];
+select '{"a": {"b":{"c": "foo"}}}'::json #> '{}';
  ?column? 
 ----------
  
@@ -883,6 +933,10 @@ select '{"a": {"b":{"c": "foo"}}}'::json #> array['a'];
  {"b":{"c": "foo"}}
 (1 row)
 
+select '{"a": {"b":{"c": "foo"}}}'::json #> array['a', null];
+ERROR:  cannot call json_extract_path with null path elements
+select '{"a": {"b":{"c": "foo"}}}'::json #> array['a', ''];
+ERROR:  cannot call json_extract_path with empty path elements
 select '{"a": {"b":{"c": "foo"}}}'::json #> array['a','b'];
    ?column?   
 --------------
@@ -949,7 +1003,7 @@ select '42'::json #> array['0'];
  
 (1 row)
 
-select '{"a": {"b":{"c": "foo"}}}'::json #>> array[]::text[];
+select '{"a": {"b":{"c": "foo"}}}'::json #>> '{}';
  ?column? 
 ----------
  
@@ -961,6 +1015,10 @@ select '{"a": {"b":{"c": "foo"}}}'::json #>> array['a'];
  {"b":{"c": "foo"}}
 (1 row)
 
+select '{"a": {"b":{"c": "foo"}}}'::json #>> array['a', null];
+ERROR:  cannot call json_extract_path_text with null path elements
+select '{"a": {"b":{"c": "foo"}}}'::json #>> array['a', ''];
+ERROR:  cannot call json_extract_path_text with empty path elements
 select '{"a": {"b":{"c": "foo"}}}'::json #>> array['a','b'];
    ?column?   
 --------------

src/test/regress/expected/jsonb.out

@@ -453,6 +453,12 @@ select '{"a": [{"b": "c"}, {"b": "cc"}]}'::jsonb -> 'z';
  
 (1 row)
 
+select '{"a": [{"b": "c"}, {"b": "cc"}]}'::jsonb -> '';
+ ?column? 
+----------
+ 
+(1 row)
+
 select '[{"b": "c"}, {"b": "cc"}]'::jsonb -> 1;
   ?column?   
 -------------
@@ -471,6 +477,50 @@ select '"foo"'::jsonb -> 1;
 ERROR:  cannot call jsonb_array_element (jsonb -> int) on a scalar
 select '"foo"'::jsonb -> 'z';
 ERROR:  cannot call jsonb_object_field (jsonb -> text) on a scalar
+select '{"a": [{"b": "c"}, {"b": "cc"}]}'::jsonb ->> null::text;
+ ?column? 
+----------
+ 
+(1 row)
+
+select '{"a": [{"b": "c"}, {"b": "cc"}]}'::jsonb ->> null::int;
+ ?column? 
+----------
+ 
+(1 row)
+
+select '{"a": [{"b": "c"}, {"b": "cc"}]}'::jsonb ->> 1;
+ERROR:  cannot call jsonb_array_element_text on an object
+select '{"a": [{"b": "c"}, {"b": "cc"}]}'::jsonb ->> 'z';
+ ?column? 
+----------
+ 
+(1 row)
+
+select '{"a": [{"b": "c"}, {"b": "cc"}]}'::jsonb ->> '';
+ ?column? 
+----------
+ 
+(1 row)
+
+select '[{"b": "c"}, {"b": "cc"}]'::jsonb ->> 1;
+  ?column?   
+-------------
+ {"b": "cc"}
+(1 row)
+
+select '[{"b": "c"}, {"b": "cc"}]'::jsonb ->> 3;
+ ?column? 
+----------
+ 
+(1 row)
+
+select '[{"b": "c"}, {"b": "cc"}]'::jsonb ->> 'z';
+ERROR:  cannot call jsonb_object_field_text (jsonb ->> text) on an array
+select '"foo"'::jsonb ->> 1;
+ERROR:  cannot call jsonb_array_element_text on a scalar
+select '"foo"'::jsonb ->> 'z';
+ERROR:  cannot call jsonb_object_field_text (jsonb ->> text) on a scalar
 -- equality and inequality
 SELECT '{"x":"y"}'::jsonb = '{"x":"y"}'::jsonb;
  ?column? 
@@ -1218,7 +1268,7 @@ SELECT '{"f2":["f3",1],"f4":{"f5":99,"f6":"stringy"}}'::jsonb#>>array['f2','1'];
 (1 row)
 
 -- corner cases for same
-select '{"a": {"b":{"c": "foo"}}}'::jsonb #> array[]::text[];
+select '{"a": {"b":{"c": "foo"}}}'::jsonb #> '{}';
  ?column? 
 ----------
  
@@ -1230,6 +1280,14 @@ select '{"a": {"b":{"c": "foo"}}}'::jsonb #> array['a'];
  {"b": {"c": "foo"}}
 (1 row)
 
+select '{"a": {"b":{"c": "foo"}}}'::jsonb #> array['a', null];
+ERROR:  cannot call jsonb_extract_path with null path elements
+select '{"a": {"b":{"c": "foo"}}}'::jsonb #> array['a', ''];
+ ?column? 
+----------
+ 
+(1 row)
+
 select '{"a": {"b":{"c": "foo"}}}'::jsonb #> array['a','b'];
    ?column?   
 --------------
@@ -1284,7 +1342,7 @@ select '42'::jsonb #> array['f2'];
 ERROR:  cannot extract path from a scalar
 select '42'::jsonb #> array['0'];
 ERROR:  cannot extract path from a scalar
-select '{"a": {"b":{"c": "foo"}}}'::jsonb #>> array[]::text[];
+select '{"a": {"b":{"c": "foo"}}}'::jsonb #>> '{}';
  ?column? 
 ----------
  
@@ -1296,6 +1354,14 @@ select '{"a": {"b":{"c": "foo"}}}'::jsonb #>> array['a'];
  {"b": {"c": "foo"}}
 (1 row)
 
+select '{"a": {"b":{"c": "foo"}}}'::jsonb #>> array['a', null];
+ERROR:  cannot call jsonb_extract_path_text with null path elements
+select '{"a": {"b":{"c": "foo"}}}'::jsonb #>> array['a', ''];
+ ?column? 
+----------
+ 
+(1 row)
+
 select '{"a": {"b":{"c": "foo"}}}'::jsonb #>> array['a','b'];
    ?column?   
 --------------

src/test/regress/expected/jsonb_1.out

@@ -453,6 +453,12 @@ select '{"a": [{"b": "c"}, {"b": "cc"}]}'::jsonb -> 'z';
  
 (1 row)
 
+select '{"a": [{"b": "c"}, {"b": "cc"}]}'::jsonb -> '';
+ ?column? 
+----------
+ 
+(1 row)
+
 select '[{"b": "c"}, {"b": "cc"}]'::jsonb -> 1;
   ?column?   
 -------------
@@ -471,6 +477,50 @@ select '"foo"'::jsonb -> 1;
 ERROR:  cannot call jsonb_array_element (jsonb -> int) on a scalar
 select '"foo"'::jsonb -> 'z';
 ERROR:  cannot call jsonb_object_field (jsonb -> text) on a scalar
+select '{"a": [{"b": "c"}, {"b": "cc"}]}'::jsonb ->> null::text;
+ ?column? 
+----------
+ 
+(1 row)
+
+select '{"a": [{"b": "c"}, {"b": "cc"}]}'::jsonb ->> null::int;
+ ?column? 
+----------
+ 
+(1 row)
+
+select '{"a": [{"b": "c"}, {"b": "cc"}]}'::jsonb ->> 1;
+ERROR:  cannot call jsonb_array_element_text on an object
+select '{"a": [{"b": "c"}, {"b": "cc"}]}'::jsonb ->> 'z';
+ ?column? 
+----------
+ 
+(1 row)
+
+select '{"a": [{"b": "c"}, {"b": "cc"}]}'::jsonb ->> '';
+ ?column? 
+----------
+ 
+(1 row)
+
+select '[{"b": "c"}, {"b": "cc"}]'::jsonb ->> 1;
+  ?column?   
+-------------
+ {"b": "cc"}
+(1 row)
+
+select '[{"b": "c"}, {"b": "cc"}]'::jsonb ->> 3;
+ ?column? 
+----------
+ 
+(1 row)
+
+select '[{"b": "c"}, {"b": "cc"}]'::jsonb ->> 'z';
+ERROR:  cannot call jsonb_object_field_text (jsonb ->> text) on an array
+select '"foo"'::jsonb ->> 1;
+ERROR:  cannot call jsonb_array_element_text on a scalar
+select '"foo"'::jsonb ->> 'z';
+ERROR:  cannot call jsonb_object_field_text (jsonb ->> text) on a scalar
 -- equality and inequality
 SELECT '{"x":"y"}'::jsonb = '{"x":"y"}'::jsonb;
  ?column? 
@@ -1218,7 +1268,7 @@ SELECT '{"f2":["f3",1],"f4":{"f5":99,"f6":"stringy"}}'::jsonb#>>array['f2','1'];
 (1 row)
 
 -- corner cases for same
-select '{"a": {"b":{"c": "foo"}}}'::jsonb #> array[]::text[];
+select '{"a": {"b":{"c": "foo"}}}'::jsonb #> '{}';
  ?column? 
 ----------
  
@@ -1230,6 +1280,14 @@ select '{"a": {"b":{"c": "foo"}}}'::jsonb #> array['a'];
  {"b": {"c": "foo"}}
 (1 row)
 
+select '{"a": {"b":{"c": "foo"}}}'::jsonb #> array['a', null];
+ERROR:  cannot call jsonb_extract_path with null path elements
+select '{"a": {"b":{"c": "foo"}}}'::jsonb #> array['a', ''];
+ ?column? 
+----------
+ 
+(1 row)
+
 select '{"a": {"b":{"c": "foo"}}}'::jsonb #> array['a','b'];
    ?column?   
 --------------
@@ -1284,7 +1342,7 @@ select '42'::jsonb #> array['f2'];
 ERROR:  cannot extract path from a scalar
 select '42'::jsonb #> array['0'];
 ERROR:  cannot extract path from a scalar
-select '{"a": {"b":{"c": "foo"}}}'::jsonb #>> array[]::text[];
+select '{"a": {"b":{"c": "foo"}}}'::jsonb #>> '{}';
  ?column? 
 ----------
  
@@ -1296,6 +1354,14 @@ select '{"a": {"b":{"c": "foo"}}}'::jsonb #>> array['a'];
  {"b": {"c": "foo"}}
 (1 row)
 
+select '{"a": {"b":{"c": "foo"}}}'::jsonb #>> array['a', null];
+ERROR:  cannot call jsonb_extract_path_text with null path elements
+select '{"a": {"b":{"c": "foo"}}}'::jsonb #>> array['a', ''];
+ ?column? 
+----------
+ 
+(1 row)
+
 select '{"a": {"b":{"c": "foo"}}}'::jsonb #>> array['a','b'];
    ?column?   
 --------------

src/test/regress/sql/json.sql

@@ -244,12 +244,24 @@ select '{"a": [{"b": "c"}, {"b": "cc"}]}'::json -> null::text;
 select '{"a": [{"b": "c"}, {"b": "cc"}]}'::json -> null::int;
 select '{"a": [{"b": "c"}, {"b": "cc"}]}'::json -> 1;
 select '{"a": [{"b": "c"}, {"b": "cc"}]}'::json -> 'z';
+select '{"a": [{"b": "c"}, {"b": "cc"}]}'::json -> '';
 select '[{"b": "c"}, {"b": "cc"}]'::json -> 1;
 select '[{"b": "c"}, {"b": "cc"}]'::json -> 3;
 select '[{"b": "c"}, {"b": "cc"}]'::json -> 'z';
 select '"foo"'::json -> 1;
 select '"foo"'::json -> 'z';
 
+select '{"a": [{"b": "c"}, {"b": "cc"}]}'::json ->> null::text;
+select '{"a": [{"b": "c"}, {"b": "cc"}]}'::json ->> null::int;
+select '{"a": [{"b": "c"}, {"b": "cc"}]}'::json ->> 1;
+select '{"a": [{"b": "c"}, {"b": "cc"}]}'::json ->> 'z';
+select '{"a": [{"b": "c"}, {"b": "cc"}]}'::json ->> '';
+select '[{"b": "c"}, {"b": "cc"}]'::json ->> 1;
+select '[{"b": "c"}, {"b": "cc"}]'::json ->> 3;
+select '[{"b": "c"}, {"b": "cc"}]'::json ->> 'z';
+select '"foo"'::json ->> 1;
+select '"foo"'::json ->> 'z';
+
 -- array length
 
 SELECT json_array_length('[1,2,3,{"f1":1,"f2":[5,6]},4]');
@@ -299,8 +311,10 @@ select '{"f2":["f3",1],"f4":{"f5":99,"f6":"stringy"}}'::json#>>array['f2','0'];
 select '{"f2":["f3",1],"f4":{"f5":99,"f6":"stringy"}}'::json#>>array['f2','1'];
 
 -- corner cases for same
-select '{"a": {"b":{"c": "foo"}}}'::json #> array[]::text[];
+select '{"a": {"b":{"c": "foo"}}}'::json #> '{}';
 select '{"a": {"b":{"c": "foo"}}}'::json #> array['a'];
+select '{"a": {"b":{"c": "foo"}}}'::json #> array['a', null];
+select '{"a": {"b":{"c": "foo"}}}'::json #> array['a', ''];
 select '{"a": {"b":{"c": "foo"}}}'::json #> array['a','b'];
 select '{"a": {"b":{"c": "foo"}}}'::json #> array['a','b','c'];
 select '{"a": {"b":{"c": "foo"}}}'::json #> array['a','b','c','d'];
@@ -313,8 +327,10 @@ select '"foo"'::json #> array['z'];
 select '42'::json #> array['f2'];
 select '42'::json #> array['0'];
 
-select '{"a": {"b":{"c": "foo"}}}'::json #>> array[]::text[];
+select '{"a": {"b":{"c": "foo"}}}'::json #>> '{}';
 select '{"a": {"b":{"c": "foo"}}}'::json #>> array['a'];
+select '{"a": {"b":{"c": "foo"}}}'::json #>> array['a', null];
+select '{"a": {"b":{"c": "foo"}}}'::json #>> array['a', ''];
 select '{"a": {"b":{"c": "foo"}}}'::json #>> array['a','b'];
 select '{"a": {"b":{"c": "foo"}}}'::json #>> array['a','b','c'];
 select '{"a": {"b":{"c": "foo"}}}'::json #>> array['a','b','c','d'];

src/test/regress/sql/jsonb.sql

@@ -113,12 +113,24 @@ select '{"a": [{"b": "c"}, {"b": "cc"}]}'::jsonb -> null::text;
 select '{"a": [{"b": "c"}, {"b": "cc"}]}'::jsonb -> null::int;
 select '{"a": [{"b": "c"}, {"b": "cc"}]}'::jsonb -> 1;
 select '{"a": [{"b": "c"}, {"b": "cc"}]}'::jsonb -> 'z';
+select '{"a": [{"b": "c"}, {"b": "cc"}]}'::jsonb -> '';
 select '[{"b": "c"}, {"b": "cc"}]'::jsonb -> 1;
 select '[{"b": "c"}, {"b": "cc"}]'::jsonb -> 3;
 select '[{"b": "c"}, {"b": "cc"}]'::jsonb -> 'z';
 select '"foo"'::jsonb -> 1;
 select '"foo"'::jsonb -> 'z';
 
+select '{"a": [{"b": "c"}, {"b": "cc"}]}'::jsonb ->> null::text;
+select '{"a": [{"b": "c"}, {"b": "cc"}]}'::jsonb ->> null::int;
+select '{"a": [{"b": "c"}, {"b": "cc"}]}'::jsonb ->> 1;
+select '{"a": [{"b": "c"}, {"b": "cc"}]}'::jsonb ->> 'z';
+select '{"a": [{"b": "c"}, {"b": "cc"}]}'::jsonb ->> '';
+select '[{"b": "c"}, {"b": "cc"}]'::jsonb ->> 1;
+select '[{"b": "c"}, {"b": "cc"}]'::jsonb ->> 3;
+select '[{"b": "c"}, {"b": "cc"}]'::jsonb ->> 'z';
+select '"foo"'::jsonb ->> 1;
+select '"foo"'::jsonb ->> 'z';
+
 -- equality and inequality
 SELECT '{"x":"y"}'::jsonb = '{"x":"y"}'::jsonb;
 SELECT '{"x":"y"}'::jsonb = '{"x":"z"}'::jsonb;
@@ -270,8 +282,10 @@ SELECT '{"f2":["f3",1],"f4":{"f5":99,"f6":"stringy"}}'::jsonb#>>array['f2','0'];
 SELECT '{"f2":["f3",1],"f4":{"f5":99,"f6":"stringy"}}'::jsonb#>>array['f2','1'];
 
 -- corner cases for same
-select '{"a": {"b":{"c": "foo"}}}'::jsonb #> array[]::text[];
+select '{"a": {"b":{"c": "foo"}}}'::jsonb #> '{}';
 select '{"a": {"b":{"c": "foo"}}}'::jsonb #> array['a'];
+select '{"a": {"b":{"c": "foo"}}}'::jsonb #> array['a', null];
+select '{"a": {"b":{"c": "foo"}}}'::jsonb #> array['a', ''];
 select '{"a": {"b":{"c": "foo"}}}'::jsonb #> array['a','b'];
 select '{"a": {"b":{"c": "foo"}}}'::jsonb #> array['a','b','c'];
 select '{"a": {"b":{"c": "foo"}}}'::jsonb #> array['a','b','c','d'];
@@ -284,8 +298,10 @@ select '"foo"'::jsonb #> array['z'];
 select '42'::jsonb #> array['f2'];
 select '42'::jsonb #> array['0'];
 
-select '{"a": {"b":{"c": "foo"}}}'::jsonb #>> array[]::text[];
+select '{"a": {"b":{"c": "foo"}}}'::jsonb #>> '{}';
 select '{"a": {"b":{"c": "foo"}}}'::jsonb #>> array['a'];
+select '{"a": {"b":{"c": "foo"}}}'::jsonb #>> array['a', null];
+select '{"a": {"b":{"c": "foo"}}}'::jsonb #>> array['a', ''];
 select '{"a": {"b":{"c": "foo"}}}'::jsonb #>> array['a','b'];
 select '{"a": {"b":{"c": "foo"}}}'::jsonb #>> array['a','b','c'];
 select '{"a": {"b":{"c": "foo"}}}'::jsonb #>> array['a','b','c','d'];