Category: 08. SQL Keys

Alternate key is a secondary key it can be simple to understand by an example: Let’s take an example of student it can contain NAME, ROLL NO., ID and CLASS. Here ROLL NO. is primary key and rest of all columns like NAME, ID and CLASS are alternate keys. If a table has more than…

A unique key is a set of one or more than one fields/columns of a table that uniquely identify a record in a database table. You can say that it is little like primary key but it can accept only one null value and it cannot have duplicate values. The unique key and primary key…

A composite key is a combination of two or more columns in a table that can be used to uniquely identify each row in the table when the columns are combined uniqueness is guaranteed, but when it taken individually it does not guarantee uniqueness. Sometimes more than one attributes are needed to uniquely identify an…

In the relational databases, a foreign key is a field or a column that is used to establish a link between two tables. In simple words you can say that, a foreign key in one table used to point primary key in another table. Let us take an example to explain it: Here are two…

A column or columns is called primary key (PK) that uniquely identifies each row in the table. If you want to create a primary key, you should define a PRIMARY KEY constraint when you create or modify a table. When multiple columns are used as a primary key, it is known as composite primary key. In designing the composite…