CREATE EXTENSION iif;
SELECT iif(1<0,1,2);
 iif 
-----
   2
(1 row)

SELECT iif(100>99, 'this is true','this is false'::text);
     iif      
--------------
 this is true
(1 row)

SELECT iif(100>99, 'this is true','this is false');
ERROR:  could not determine polymorphic type because input has type unknown
SELECT iif(1>0, 'this is true'::text,'this is false');
     iif      
--------------
 this is true
(1 row)

SELECT iif(NULL, 'this is true'::text,'this is false');
 iif 
-----
 
(1 row)