i have a few columns that i know won't be used initially. is it a good practice to add columns only when needed or just leave those extra columns there?
is it just a little more space in the header or every row?
A:
Depends on the column type to some extent.
Variable sized columns (such as varchar(nn)) will only use 4 bytes (approx) per row.
I would add columns only when required, since it is less likely that redundant columns will be added and never removed.
Mitch Wheat
2009-05-10 03:45:29
even when they are empty? or nullmy question should be does empty or null fields take up space
2009-05-10 03:49:59
Yes. Empty and NULL columns do take up space. SQL Server 2008 has new row compression for sparse tables, i.e. those with lots of NULL columns...
Mitch Wheat
2009-05-10 04:16:30
Unless you have Huge tables, I think the maintainability issue of redundant columns is more important that space concerns. I often see DBs with may unused columns but developers are nervous to remove in case they are used somewhere else (such as export to another system etc)
Mitch Wheat
2009-05-10 04:18:27
A:
Yes, they do still take up space, if only a couple bytes per row (depends on the column type). If you're not going to use them until later, what good is it to keep them there?
musicfreak
2009-05-10 04:01:21