MariaDB Null Values - MariaDB

What are NULL values in MariaDB?

It is important fact that NULL values are unknown values. But they are not considered as empty strings or zero, but they are valid values. While Null values in table creation, column specifications allow for setting them to accept or reject them. So employ a NULL or NOT NULL clause. This has applications in cases of missing record information like an ID number.
It is mentioned that many user-defined variables have a value of NULL until explicit assignment. Stored routine parameters and local variables allow setting a value of NULL. It has a value when a local variable has no default value.
NULL is case-insensitive, and has the following aliases −
  • UNKNOWN (a boolean value)
  • \N

NULL Operators

Standard comparison operators cannot be used with NULL (e.g., =, >, >=, <=, <, or !=) because all comparisons with a NULL value return NULL, not true or false. Comparisons with NULL or possibly containing it must use the “<=>” (NULL-SAFE) operator.
Other available operators are −
  • IS NULL − It tests for a NULL value.
  • IS NOT NULL − It confirms the absence of a NULL value.
  • ISNULL − It returns a value of 1 on discovery of a NULL value, and 0 in its absence.
  • COALESCE − It returns the first non-NULL value of a list, or it returns a NULL value in the absence of one.

How to sort NULL Values?

In sorting operations, NULL values have the lowest value, so DESC order results in NULL values at the bottom. MariaDB allows for setting a higher value for NULL values.
There are two ways to do this as shown below –
The other way –

NULL Functions

Get NULL output when the parameters are NULL. Below mentioned functions are specifically designed for managing NULL values. They are −
  • IFNULL() − If the first expression is not NULL it returns it. When it evaluates to NULL, it returns the second expression.
  • NULLIF() − It returns NULL when the compared expressions are equal, if not, it returns the first expression.
Usually, functions like SUM and AVG ignore NULL values.

How to insert NULL Values?

When you insert a NULL value in a column is specified as NOT NULL, an error occurs. But in a default SQL mode, a NOT NULL column will insert a default value based on data type.
When a field is a TIMESTAMP, AUTO_INCREMENT, or virtual column, MariaDB manages NULL values differently. Insertion in an AUTO_INCREMENT column causes the next number in the sequence to insert in its place. In a TIMESTAMP field, MariaDB assigns the current timestamp instead.
UNIQUE indices can hold many NULL values, however, primary keys cannot be NULL.

NULL Values and the Alter Command

While, WMariaDB automatically assigns values when you use the ALTER command to modify a column in case of NULL specifications.

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