SELECT NULL

First of all we should know that what null value is? Null values are used to represent missing unknown data.

There can be two conditions:

1. Where SQL is NULL
2. Where SQL is NOT NULL

If in a table, a column is optional, it is very easy to insert data in column or update an existing record without adding a value in this column. This means that field has null value.

Note: we should not compare null value with 0. They are not equivalent.

Where SQL is NULL:

How to select records with null values only? (in the marks column)

There is an example of student table:

SIR_NAME	NAME	MARKS
TYAGI	SEEMA
SINGH	RAMAN	5.5
SHARMA	AMAR
JAISWAL	VICKY	6.2

Let’s see the query to get all the records where marks is NULL:

SELECT SIR_NAME, NAME, MARKS FROM STUDENTS  

WHERE MARKS IS NULL

It will return the following records:

SIR_NAME	NAME	MARKS
SHARMA	AMAR
TYAGI	SEEMA

Where SQL is NOT NULL:

How to select records with no null values(in marks column)? Let’s see the query to get all the records where marks is NOT NULL

SELECT SIR_NAME, FIRSTNAME, MARKS FROM STUDENTS    

WHERE MARKS IS NOT NULL   

SIR_NAME	NAME	MARKS
SINGH	RAMAN	5.5
JAISWAL	VICKY	6.2