NOT NULL in SQL

NOT NULL constraints:

                                        The NOT NULL constraints restricts null value in database table.

Syntax:

                CREATE TABLE Employee(id int, emp_name nvarchar(18) NOT NULL);

This statement create table employee, in that emp_name should not be null value.

DESC Employee

Desc statement describe the table. 

Field	Data Type	Null	key	Default
id	INT	NO
emp_name	NVARCHAR(18)	NO

               CREATE TABLE Course(id int NOT NULL, Course_name nvarchar(20));

Desc Course (in Oracle) 

Field	Data Type	Null	key	Default
id	INT	NO
Course_name	NVARCHAR(20)	NO

Using Alter to Set NOT NULL:

ALTER TABLE course ALTER COLUMN Course_name nvarchar(20) NOT NULL; in MSSQL server.

ALTER TABLE Course MODIFY Course_name  nvarchar(20) NOT NULL; in ORACLE.

ALTER TABLE Course MODIFY COLUMN Course_name nvarchar(20) NOT NULL; in MSACCESS.

Desc Course.

Field	Data Type	Null	key	Default
id	INT	NO
Course_name	NVARCHAR(20)	NO

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