Unknown returned type in PostgreSQL query
You can do this without generating a warning by creating a type and casting the records to it:

create type t as (a integer, b varchar(255));

select * from unnest(array[(1,'hello'), (3,'world')]::t[]);
┌───┬───────┐
│ a │   b   │
├───┼───────┤
│ 1 │ hello │
│ 3 │ world │
└───┴───────┘


tested on 9.4 and 9.3 (db&lt;>fiddle here)