Why are null values not used in a database?
I disagree about the usage of NULL values in a database. NULL values are an important factor in DB design. Actually you should not allow to store empty strings in a varchar (char, text, etc) field. As you said, a NULL value means “does not exist”.
When is the first name not set in a database?
When creating the user, the person will see 2 text inputs, one for first and one for last. The person chooses to only enter the last name. The first name is technically not set. During the insert I check the length of each field, setting all fields that are empty to NULL. When looking at the database, I see that the first name is not set.
What’s the difference between null and empty in SQL?
In SQL, the formally more correct solution was adopted. An empty field, if it doesn’t have a default value or if it’s cleared by the user, is “Null”. Null, another word meaning zero, doesn’t behave like Empty. Quite the opposite: every expression involving Null becomes Null (with a few exceptions).
Why is the section about null bigger than the others?
The section about Null is larger than the others, due to a personal bias towards databases, but also because, among the keywords for absence, Null raises the most questions on Experts-Exchange. [I must confess: not all puns in the article were intended, not quite…]
Is it possible to null a column in a data model?
There is a balance, though – not every column in your data model should be nullable. There are often optional fields on a form, or pieces of information that otherwise don’t get collected at the time the row is created. But that doesn’t mean you can defer populating all of the data.
Why are null able columns bad for performance?
NULL’able columns are a disaster from a performance perspective. Consider integers arithmetic as an example. In a sane world without NULL, it is “easy” to vectorise integer arithmetic in the database engine code using SIMD instructions to perform pretty much any calculation at speeds faster than 1 row per CPU cycle.
Why are nulls not an intrinsic data type?
NULL is not a value, and therefore has no intrinsic data type. Nulls need special handling all over the place when code that otherwise relies on actual types might also receive the un-typed NULL.