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When designing a database are NULLs OK?
33 Answers. Nulls are negatively viewed from the perspective of database normalization. The idea being that if a value can be nothing, then you really should split that out into another sparse table such that you don’t require rows for items which have no value. It’s an effort to make sure all data is valid and valued.
Why having NULL values in your database is a problem?
In practice, the most common solution for this particular problem is to mark those missing values as NULL. A NULL value is a special marker used in SQL to indicate that a data value does not exist in the database. In other words, it is just a placeholder to denote values that are missing or that we do not know.
Do NULL values take up space?
If the field is variable width the NULL value takes up no space. In addition to the space required to store a null value there is also an overhead for having a nullable column. For each row one bit is used per nullable column to mark whether the value for that column is null or not.
When should you use NULL?
Allow null only if it makes sense for an object reference to have ‘no value associated with it’. Don’t use null to signal error conditions. The concept of null exists only for reference types. It doesn’t exist for value types.
What does the null value mean in a database?
unknown value
In terms of the relational database model, a NULL value indicates an unknown value. If we widen this theoretical explanation, the NULL value points to an unknown value but this unknown value does not equivalent to a zero value or a field that contains spaces.
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”.
What are the pros and cons of null values?
A column that allows NULL values also allows rows to be inserted with no values at all in that column. There are several pros and cons of using NULL values as opposed to default values: NULL value does not have the data type, therefore can be inserted to any data structure and any database column.
What’s the difference between null and default values?
NULL value does not have the data type, therefore can be inserted to any data structure and any database column. Default values, on the other hand, need to have their data type specified and a default value in one column might look the same in another column, but it might be of a different type.
How much storage does a null value take?
A NULL value in databases is a system value that takes up one byte of storage and indicates that a value is not present as opposed to a space or zero or any other default value.