Chars, varchars and not nulls

[eramgarden]

Second week at my new job and looking at the DB :)

 

1.They have made every field either char or numeric or created user-defined database type.

Read about the diff between char and varchar:Char being faster and it's used for "fixed length" if it's less than 30 bytes. Varchar used for "variable length".

 

2. They have made ALL char fields NOT NULL with default value of BLANK.

 

Questions

 

1. Still not sure what variable length and fixed length mean. How would I know if the data is less than 30 bytes?

 

2. Is there a downside to making everything NOT Null and having default of blank?