NULL emements lost when casting result of unnest()

Question

I stumbled upon very odd behavior with unnest(), when casting after expanding an array.

Introduction

There are three basic syntax variants to use unnest():

Answer 1

Casting SRF function (in FROM clause) is not supported - you cannot use any operator there. Only function call is allowed.

a cast is possible only in column list:

postgres=# SELECT * FROM unnest('{2,NULL,1}'::int[])::text;
ERROR:  syntax error at or near "::"
LINE 1: SELECT * FROM unnest('{2,NULL,1}'::int[])::text;
                                                 ^
postgres=# SELECT v::text FROM unnest('{2,NULL,1}'::int[]) g(v);
   v    
────────
      2
 [null]
      1
(3 rows)

Missing row from NULL is probably bug and should be reported

postgres=# SELECT unnest('{1,NULL,4}'::int[])::text;
 unnest 
────────
      1
 [null]
      4
(3 rows)

postgres=# SELECT unnest('{1,NULL,4}'::int[])::numeric;
 unnest 
────────
      1
      4
(2 rows)

There is not reason, why NULL rows should be dropped, I think