1. NOT NULL: it species that a column can never have null values, i.e., not empty
2. UNIQUE: it ensures that no two rows have same value in the specified column.
3. PRIMARY KEY: it declares a column or a set of columns as the primary key of the table. This constraint makes a column NOT NULL and UNIQUE.
4. DEFAULT: it sets a default value for a column when the user does not enter a value for that column.
5. Auto_increment: This constraint is used to perform auto_increment the values in a column. That is automatically generate serial numbers. Only one auto_increment column per table is allowed.
