1.7 Null Values

Question 1

NULL

Answer 1

NULL is a special value that represents either unknown or inapplicable data.

NULL is not the same as zero for numeric data types or blanks for character data types. Ex: A zero bonus indicates an employee can, but has not, earned a bonus. A zero bonus is known and applicable, and should not be represented as NULL.

Question 2

NOT NULL constraint

Answer 2

The NOT NULL constraint prevents a column from having a NULL value. Statements that insert NULL, or update a value to NULL, are automatically rejected.

Name VARCHAR(60) NOT NULL

Question 3

Logical operators to check for NULL values

Answer 3

IS NULL and IS NOT NULL logical operators must be used to select NULL values.

Question 4

truth tables

Answer 4

The value of logical expressions containing NULL operands is defined in truth tables.

Question 5

Why can’t you use = NULL to check for a NULL value?

Answer 5

Because = is an arithmetic operator and this needs a comparison operator