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Start your free trialHanna Han
4,105 PointsColumns that are able to have null values
Hi,
I wonder there are any rules on what kind of column should have a value present or can have NULL value. Is it database designers that can control over it when they create database or there are specific type of values we need to know to distinguish those two different kinds?
1 Answer
Steven Parker
231,184 PointsThe decision to allow NULL or not is part of the design. Any column that serves as an index, identifier, or provides a foreign key for relationships will be designed to not allow NULL values.
Otherwise, it becomes a decision based on what makes sense for the kind of data being stored in the column. A table of poll responses, for example, might use NULL to represent "no answer" to a question.
Alexis Ruiz
9,237 PointsAlexis Ruiz
9,237 PointsBut how can we know which one is allowed and which one is not?
Steven Parker
231,184 PointsSteven Parker
231,184 PointsAs a designer, you get to decide when to allow them based on what you are using each column for.