Removing default NULL from table definition

[Andrey Kondakov]

Hi,

I am trying to optimize table structure according to optimization tips in mysql documentation. Currently most of columns in my table use "default NULL" clause. I see that it's not recommended by optimization guide.
Here I'm a little bit confused, since I don't get exactly which value is necessary to use if a column really needs to have default value.

Say, I have int and varchar columns:
serverTime bigint(20) default NULL
serverName varchar(50) default NULL

I wish to get rid of NULL's and change the columns to:
serverTime bigint(20) default 0
serverName varchar(50) default ''

Is it better than having NULL's? Is it that MySQL optimization guide recommends to do?

Thanks,

Andrey