With suitable syntax and examples, implement the following constraints in the database of your chosen domain (explain syntax in comment)Primary KeyForeign KeyNULLNOT NULLCHECKUNIQUEAUTO_INCREMENTDEFAULT- Change an existing NOT NULL column to NULL  using alter command.

Sure, I will use SQL (Structured Query Language) to explain the implementation of these constraints. SQL is a standard language for managing data held in a relational database management system.

1. Primary Key: A primary key is a field in a table which uniquely identifies each row/record in a database table. Primary keys must contain unique values. A primary key column cannot have NULL values.

CREATE TABLE Students (
    StudentID int NOT NULL,
    LastName varchar(255) NOT NULL,
    FirstName varchar(255),
    Age int,
    PRIMARY KEY (StudentID)
);

2. Foreign Key: A foreign key is a field (or collection of fields) in one table, that is used to refer to the primary key in another table. The table with the foreign key is called the child table, and the table with the primary key is called the referenced or parent table.

CREATE TABLE Orders (
    OrderID int NOT NULL,
    OrderNumber int NOT NULL,
    PersonID int,
    PRIMARY KEY (OrderID),
    FOREIGN KEY (PersonID) REFERENCES Persons(PersonID)
);

3. NULL: A NULL value in a table is a value in a field that appears to be blank, which means it is a field with no value.

CREATE TABLE Students