ghowe=# select unnest(ARRAY[1,2],ARRAY['foo','bar','baz']); ERROR: function unnest(integer[], text[]) does not exist LINE 1: select unnest(ARRAY[1,2],ARRAY['foo','bar','baz']) ^ HINT: No function matches the given name and argument types. You might need to add explicit type casts.
As your query doesn't place the unnest function in the FROM clause as the documentation says is required it is to be expected that your query fails. The subsequent part of that sentence links you over to the section of the documentation that provides a full example. The one in the table is intended as a quick-reference.
