In this article, we will learn how to use the Foreign Key constraint in SQL.
A FOREIGN KEY is a key, used to link tables together.
In this article, we will learn how to use the Primary Key constraint in SQL.
The PRIMARY KEY constraint is used to identify each record uniquely in a table.
In this article, we will learn how to use the UNIQUE constraint in SQL.
The UNIQUE constraint is used to ensure that all values in a column are different.
In this article, we will learn how to use the NOT NULL constraint in SQL.
A column can hold NULL values by default. The NOT NULL constraint is used to enforce a column to NOT accept NULL values.
In this article, we will learn how to use the ALTER TABLE statement in SQL.
To add or delete or modify columns in an existing table, the ALTER TABLE statement is used.
The ALTER TABLE statement also can be used to add or drop various constraints on an existing table.
