Question

I was reading Django Book and came across interesting statement.

Notice that Django doesn’t use SELECT * when looking up data and instead lists
 all fields explicitly. This is by design:
 in certain circumstances SELECT * can be slower,

I got this from http://www.djangobook.com/en/1.0/chapter05/

So my question is can someone explain me why SELECT * can be slower, than call every single column explicitly. Would be good if you can give me some examples.
Or if you think the opposite (it doesn’t matter), can you explain why?

Update:

That’s the table :

BEGIN;
CREATE TABLE "books_publisher" (
    "id" serial NOT NULL PRIMARY KEY,
    "name" varchar(30) NOT NULL,
    "address" varchar(50) NOT NULL,
    "city" varchar(60) NOT NULL,
    "state_province" varchar(30) NOT NULL,
    "country" varchar(50) NOT NULL,
    "website" varchar(200) NOT NULL
);

And that’s how Django will call SELECT * FROM book_publisher:

SELECT
    id, name, address, city, state_province, country, website
FROM book_publisher;

Answer 1

1. performance (will matter only if you are selecting less columns than there are in the table
2. I am not sure about how Django works; but in some languages/ db drivers “select *” will cause an error if you change the table schema (say add a new column). This is because the DB driver “caches” the table schema and now its internal schema does not match the table schema.