Not Null in DBMS

January 31, 2023

NOT NULL

On this page we will discuss about NOT NULL in DBMS. Once not null is applied to a particular column, you cannot enter null values to that column and restricted to maintain only some proper value other than null It is an important concept of DBMS.So, lets just discuss it in detail.

NOT NULL IN DBMS

Null value is different from zero value or a field that contain spaces
Null represents a record where data may be missing data or data for that record may be optional
Not all constraints prevents a column to contain null values
Once not null is applied to a particular column, you cannot enter null values to that column and restricted to maintain only some proper value other than null
A not-null constraint cannot be applied at table level

What is Database

Participation Constraint

DBMS Architecture

Data Models

Cardinality

Syntax

CREATE TABLE table_name
(
   column1 datatype(size),
   column2 datatype(size),
   column3 datatype(size) NOT NULL ,
);

Example

CREATE TABLE STUDENT 
(
   ID   INT             NOT NULL,
   NAME VARCHAR (20)     NOT NULL,
   AGE  INT             NOT NULL,
   ADDRESS  CHAR (25) ,
   SALARY   DECIMAL (18, 2),       
   PRIMARY KEY (ID)
);

In the above example, we have applied not null on three columns ID, name and age which means whenever a record is entered using insert statement all three columns should contain a value other than null
We have two other columns address and salary, where not null is not applied which means that you can leave the row as empty or use null value while inserting the record into the table

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