svanderclock wrote:
In an index where around 20% of values are null, what is better, to put null or an empty string ? Or it doeasn't matter?
Ann W. Harrison answers:
In terms of storage, it doesn't matter. Prefix compression gets rid of duplicates - null, empty, or full. NULL has some advantages in terms of index ordering - they can be first, last, high, or low. But I would use NULL only when the value is not known, and empty strings when the value is known not to exist.