What is the difference between a column-level constraint and a row-levelconstraint? Describe the SQL clauses used in the definition of:(a) a primary key constraint(b) an alternate key constraint(c) a foreign key constraint(d) a check constraint

Column-level constraints are applied only to one column, whereas row-level constraints are applied to the whole row in the table.

(a) A primary key constraint: This is a column-level constraint where a column or set of columns is defined as the primary key for the table. The primary key uniquely identifies each record in the table. In SQL, it is defined using the PRIMARY KEY clause. For example:

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

(b) An alternate key constraint: This is a column-level constraint where a column or set of columns is defined as an alternate key for the table. The alternate key also uniquely identifies each record in the table. In SQL, it is defined using the UNIQUE clause. For example:

CREATE TABLE Students (
    StudentID int NOT NULL,
    StudentName varchar(255) NOT NULL UNIQUE,
    Age int
);

(c) A foreign key constraint: This is a column-level constraint where a column or set of columns is defined as a foreign key. The foreign key is a key used to link two tables together. In SQL, it is defined using the FOREIGN KEY clause. For example:

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

(d) A check constraint: This is a column-level or row-level constraint that allows you to specify a condition on a column or set of columns that the data entered into the table must meet. In SQL, it is defined using the CHECK clause. For example:

CREATE TABLE Students (
    StudentID int NOT NULL,
    StudentName varchar(255) NOT NULL,
    Age int CHECK (Age>=18)
);