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SQL 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:

  1. SELECT SIR_NAME, NAME, MARKS FROM STUDENTS
  2. 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

  1. SELECT SIR_NAME, FIRSTNAME, MARKS FROM STUDENTS
  2. WHERE MARKS IS NOT NULL
SIR_NAME NAME MARKS
SINGH RAMAN 5.5
JAISWAL VICKY 6.2
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