How MySQL Uses Indexes

[mathieu]

Hi,

I don't know if I'd rather post this topic in the newbie section or in this one, I hope you don't mind if I'm mistaken.

I'm reading the mysql documention about indexes, and I don't understand the following part of the "How MySQL Uses Indexes" chapter.

"without an index, MySQL has to start with the first record and then read through the whole table to find the relevant rows."

Does it mean that, without an index, mysql will seek the data through the whole row, even the fields that are not selected or that don't appear in the where clause ?

Cause, as I don't understand this part, I can neither understand the following one :
"If a table has 1,000 rows, this is at least 100 times faster than reading sequentially. Note that if you need to access almost all 1,000 rows, it is faster to read sequentially, because that minimizes disk seeks."

thanks