Sql NULL Values

What is NULL value?

The SQL NULL is the term used to represent a missing value. A field with a NULL value is a field with no value.
If in a table for any column you don't want to insert any value Then the field will be saved with a NULL value.
It is very important to understand that a NULL value is different than zero value or a field that contains spaces.

HOW TO TEST FOR NULL VALUES:-

It is not possible to test for NULL values with comparison operators ,such as = , > ,< or < > .
So you will have to use IS NULL and IS NOT NULL operators instead.

SYNTAX:-

IS NULL SYNTAX:-

SELECT column_names
FROM table_name
WHERE column_name IS NULL;

IS NOT NULL SYNTAX:-

SELECT column_names
FROM table_name
WHERE column_name IS NOT  NULL;

Consider the following EMPLOYEE table having the records as shown below:-

The IS NULL Operator:-

 The IS NULL operator is used to test for NULL values.
The following example lists all EMPLOYEE with a NULL value in the "SALARY" field:-

EXAMPLE:-

SELECT  NAME, AGE ADDRESS 
FROM EMPLOYEE
WHERE SALARY IS NULL;

OUTPUT:-



The IS NOT NULL Operator:- 

The IS NOT NULL operator is used to test for non-empty values.

The following Example lists all EMPLOYEE with a NULL value in the "SALARY" field:- 

EXAMPLE:-

SELECT ID, NAME, AGE, ADDRESS, SALARY

FROM EMPLOYEE

WHERE SALARY IS NOT NULL;

OUTPUT:-



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