Any arithmetic expression containing a null always evaluates to null. For example, null added to 10 is null. In fact, all operators (except concatenation) return null when given a null operand. And this is required by the SQL standard.

What NULL 10?

If a column in a row has no value, then the column is said to be null, or to contain null. For example, null added to 10 is null. ... In fact, all operators (except concatenation) return null when given a null operand.

What is NULL statement in SQL?

The NULL statement is an executable statement that does nothing. The NULL statement can act as a placeholder whenever an executable statement is required, but no SQL operation is wanted; for example, within a branch of the IF-THEN-ELSE statement.