SELECT build_json_array('a',1,'b',1.2,'c',true,'d',null,'e',json '{"x": 3, "y": [1,2,3]}');
                           build_json_array                            
-----------------------------------------------------------------------
 ["a", 1, "b", 1.2, "c", true, "d", null, "e", {"x": 3, "y": [1,2,3]}]
(1 row)

SELECT build_json_object('a',1,'b',1.2,'c',true,'d',null,'e',json '{"x": 3, "y": [1,2,3]}');
                             build_json_object                              
----------------------------------------------------------------------------
 {"a" : 1, "b" : 1.2, "c" : true, "d" : null, "e" : {"x": 3, "y": [1,2,3]}}
(1 row)

SELECT build_json_object( 
       'a', build_json_object('b',false,'c',99), 
       'd', build_json_object('e',array[9,8,7]::int[],
           'f', (select row_to_json(r) from ( select relkind, oid::regclass as name from pg_class where relname = 'pg_class') r)));
                                        build_json_object                                        
-------------------------------------------------------------------------------------------------
 {"a" : {"b" : false, "c" : 99}, "d" : {"e" : [9,8,7], "f" : {"relkind":"r","name":"pg_class"}}}
(1 row)

-- empty objects/arrays
SELECT build_json_array();
 build_json_array 
------------------
 []
(1 row)

SELECT build_json_object();
 build_json_object 
-------------------
 {}
(1 row)

-- make sure keys are quoted
SELECT build_json_object(1,2);
 build_json_object 
-------------------
 {"1" : 2}
(1 row)

-- keys must be scalar and not null
SELECT build_json_object(null,2);
ERROR:  arg 1: key cannot be null
SELECT build_json_object(r,2) FROM (SELECT 1 AS a, 2 AS b) r;
ERROR:  key value must be scalar, not array, composite or json
SELECT build_json_object(json '{"a":1,"b":2}', 3);
ERROR:  key value must be scalar, not array, composite or json
SELECT build_json_object('{1,2,3}'::int[], 3);
ERROR:  key value must be scalar, not array, composite or json