CODEWITHSUNDEEP
database
Madheena
Madheena

Reputation:

What does a null value in DBMS represent?

What does a null value in DBMS represent?

Is it unassigned or inapplicable or zero or blank space?

Upvotes: 2

Views: 7240

Answers (3)

Singamsetti Taraka Swathi
Singamsetti Taraka Swathi

Reputation: 1

Special value that is supported by SQL is called as null which is used to represent values of attributes that are unknown or do not apply for that particular row

For example age of a particular student is not available in the age column of student table then it is represented as null but not as zero It is important to know that null values is always different from zero value A null value is used to represent the following different interpretations

Value unknown (value exists but is not known)

Value not available (exists but is purposely hidden)

Attribute not applicable (undefined for that row)

Upvotes: 0

user3027894
user3027894

Reputation: 11

I'm a student, also preparing myself for OCA now-days. As far as nulls are concerned the first thing to be kept in mind is that null is not a value. in the world of DBMS there are only two things either it has a value or it has a null. there are some points about null:-

  • null is not a value.
  • it is not compared with any value.
  • it doesn't occupy any space.
  • when we use null in our queries we have to associate it as "is & as".

For example:-

select * from employee 
where 
salary is null

note:- we can't write queries like,

select * from employee
where 
salary=null:

(here "=" doesn't work)

Upvotes: 1

Learning
Learning

Reputation: 8175

Null is a special marker used in SQL to indicate that a data value does not exist in the database. Introduced by the creator of the relational database model, E. F. Codd, SQL Null serves to fulfill the requirement that all true RDBMS support a representation of missing information and/or inapplicable information

More info here

Upvotes: 11

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