See a blog post today, it wrote:
fixed length table will improve performance, because MySQL search will be quicker, because these fixed length is easy to calculate the next of the deviation of the data, so the reading of the natural also will soon, but if the field is not fixed, so every time looking for the next article, need program to find the primary key,

Want to ask is, MySQL in the implementation of the SELECT operation, what is the working principle,
Such as performing

 SELECT fixed-length fields 

 SELECT variable-length field 

Different in the two queries from time to tome what?