Null in mysql

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Report Error. In order to meet the requirements of true relational database management systems, MySQL uses NULL as the place holder for the values that have not been submitted. The screenshot below shows how NULL values look in database.

The NOT logical operator is used to test for Boolean conditions and returns true if the condition is false. The NOT operator returns false if the condition been tested is true. There will be cases when we will have to perform computations on a query result set and return the values. Performing any arithmetic operations on columns that have the NULL value returns null results. In order to avoid such situations from happening, we can employ the use of the NOT NULL clause to limit the results on which our data operates.

The employee number should always be supplied.