Why does a column in a table have NULL values?
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Why does a column in a table have NULL values?
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A column in a table can have NULL values for two specific reasons:
- It could be that the value of the attribute is not known. For example, a newly hired employee might not have a project to work on the very first day of joining. Therefore, the project attribute of that particular record will be NULL.
- It could be that there is no appropriate value to give the attribute for a given instance. For example, the Employee entity has an attribute Commission, which is applicable to only those employees who are working in sales. Therefore, the value of this particular attribute for all those employees who are not in sales will be NULL.
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