Not Null in DBMS

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