not null sql

1SELECT column_name FROM table_name 
2WHERE column_name IS NOT NULL;

1SELECT column_names
2FROM table_name
3WHERE column_name IS NOT NULL;

1SELECT column_name FROM table_name 
2WHERE column_name IS NULL;

1SELECT * FROM my_table WHERE my_column IS NOT NULL;

1The reverse of NULL. Tests for values that aren’t empty / NULL
2"Tests for empty (NULL) values.
3Example: Returns users that haven’t given a contact number.
4SELECT * FROM users
5WHERE contact_number IS NULL;"

1By default, a column can hold NULL values.
2The NOT NULL constraint enforces a column to NOT accept NULL values.
3This enforces a field to always contain a value, which means that you cannot insert a new record, or update a record without adding a value to this field.
4
5Sql NOT NULL in creating a table
6CREATE TABLE Persons (
7    ID int NOT NULL,
8    LastName varchar(255) NOT NULL,
9    FirstName varchar(255) NOT NULL,
10    Age int
11);