Hi,

I've a table and a column in this table will only be used/has a value for about 1% of all records.
What will be the best design priciple for such a column?

cheers
Charlie

either
define the column, and allow null values
OR
take a more zealous approach (if you believe all nulls are bad) and create a table just to hold that one value.

the second approach is probably more space efficient (as you only store the column when required, although there will be some negligible overhead)
the first approach probably more run time efficient (as there is one less join to process).

there are those who advocate that null brakes the rules of relational db design.
...and there are those who don't believe that a NULL value has any place in a DB schema
...and there are those who think NULL's are perfectly acceptable values (as long as you now why you are allowing NULL's in the first place and handle them correctly)

What is the datatype of the column?
Space is likely not a significant concern. I'd almost always recommend option 1, not being a "null purist".

certainly slows 'em down a bit, eh

oops sorry about that, been playing to much wordscraper.....

...been playing too much wordscraper....