i create a table and in thai table have one field that field usually have NULL values. is performance of my database has been down

ex of my db

field1 field2 field3
001 001 NULL
002 003 NULL
004 001 a
005 006 NULL

like this is performance of my db is poor ?

forgive my english i'm not good in english

what is the problem you think may exist
what made you ask the question

on the face of it the desing looks fine
the only problem I can see would be calling your column (field) names field1, field2, field3 - its generally better practise to give them meaningfull names. For example for a table holding an address

AddressLine1 or AddrLine1
AddressLine2 or AddrLine2
AddressLine3 or AddrLine3
AddressLine4 or AddrLine4
AddressLine5 or AddrLine5
PostCode
Country

alternatively
AddressLine1 or AddrLine1
AddressLine2 or AddrLine2
Town
City
County
PostCode
Country

in my view the only possible problem is how you have defined the 3rd column, the one that stores the nulls - does the db you are using support a varaible length datatype (memo, varchar etc...), and if so are you using that data type. It doenn't matter if the column size is small but if its large then it could have a slight impact on performance.
...and that problem only relates to storage and may have a minor impact on retrieval performance.

explore

i use MS SQL Server 200 and design my database for my explore

in my explore form have 5 question and user can comment anything to me my database is like this

AnswerOfQuestion_01
AnswerOfQuestion_02
AnswerOfQuestion_03
AnswerOfQuestion_04
AnswerOfQuestion_05
CommentToMe

people seldom fill comment to me it make my databse have a lot of NULL value in filed CommentToMe

i want to know this make performance of my database come poor
it have only one problem that it will have a bigger size, that right ?
it don;t make my database slower ?

sorry, if i ask my question don't clear

thank you for your answer