Example Of Unique Key In Sql

A unique key in SQL is the set of fields or columns of a table that helps us uniquely identify records. The unique key guarantees the uniqueness of the columns in the database. Examples to find a unique key in SQL by checking the constraint type. Using the following query, we can also find all the UNIQUE constraints in a table.

It is also possible to define a unique key on multiple columns. Let's see an example of how this works. Defining a Unique Key on Multiple Columns. In the previous example, we implemented a unique key constraint on the PhoneNumber column and on the Email column separately. This meant that each column separately had to store unique values.

The SQL Unique Key. The SQL Unique Key or, Unique constraint does not allow duplicate values in a column of a table. It prevents two records from having same values in a column. Unique Key is just an alternative to the Primary Key as both Unique and Primary Key constraints ensure uniqueness in a column of the table.

While similar to a primary key, a unique key differs in that a table can have multiple unique keys, and these keys can contain NULL values though only one NULL per column is allowed in many RDBMSs. Example In a Users table, the Email column might be a unique key with a UNIQUE constraint to ensure that no two users have the same email address

In the above example, Roll_no can act as a primary since it is unique and there is no null value. Personal_id can act as a unique key because it is also unique and for one time we can keep its value as null so Personal_id is a unique key.. Advantages of Unique Key . As we have discussed above, a unique key is used to remove duplicity in the table. A unique key helps to maintain the data

Creating SQL Unique Key Rolling Out the Red Carpet. There are two main ways to create a Unique Key When creating a new table In this example, we're creating an Employees table. The Email column has a UNIQUE constraint, ensuring no two employees can have the same email address. 2. Adding a Unique Key to an Existing Table

Constraint_name Name of the unique key which you want to delete. Example 3 - To Remove of Unique Key Constraints. Let's look at an example of removing a unique key constraint in SQL Server using the DROP TABLE statement. ALTER TABLE HeadofDepts DROP CONSTRAINT unique_hod Output

SQL UNIQUE Constraint. The UNIQUE constraint ensures that all values in a column are different.. Both the UNIQUE and PRIMARY KEY constraints provide a guarantee for uniqueness for a column or set of columns.. A PRIMARY KEY constraint automatically has a UNIQUE constraint.. However, you can have many UNIQUE constraints per table, but only one PRIMARY KEY constraint per table.

It then defines a SQL unique key constraint, named 'pk_students', which ensures that the combination of values in the first_name, last_name, and email columns must be unique across the table. This means that no two students can have the same first name, last name, and email address. SQL UNIQUE KEY Constraint on ALTER TABLE

When designing a database, Primary Keys and Unique Keys are two fundamental constraints that ensure data integrity and consistency. Both are essential in structuring a reliable database, but they serve distinct purposes. In this guide, we'll explore the differences, similarities, and use cases of Primary Keys and Unique Keys, along with practical SQL examples.