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Primary Key In SQL

Primary Key In SQL


SQL has become one of the most demanding skill sets in the programming world. These databases provide a high quality of information, and this multipurpose database is essential for generating large databases no matter what the size. SQL consists of different types of languages like data definition language, data manipulation language, and data query language. The scope of SQL is vast and multi formative.

Why should you use SQL?

SQL is quite a popular language program and is used by thousands of programmers and developers every day. This program helps a programmer to describe the data and access it in the database management systems. This program helps you to create and drop databases and tables and view the stored process and functions inside the databases. It can be efficiently used with other languages and set permissions on tables, views, and procedures.

The process of SQL

SQL engines figure out to interpret the task and execute commands for any RDBMS and figures out the best way to carry the request to the drivers. The system uses Query Dispatcher, Optimization engines, Classic Query Engines and SQL Query Engines as components for running the program.

Some of the most prominent features of SQL are:


Most of the relational databases.It is easier for you to create an extension using this language. This makes SQL a beast in the relational database systems.

Management Large Data

SQL is used in large databases with select, create, insert, drop, update and delete functions and so it helps in managing the data volume with ease and efficiency.

Gain Access to Database

SQL can be used by large as well as small organizations to develop their apps and gain access. The size of the organization doesn’t matter in SQL and works for all types.

Flexibility of Use

SQL is an open-source program, and it can be adapted for multiple uses and can be easily ported to various devices with complete ease and flexibility.

Top Performance

SQL can use in substantial workload places and is capable of withstanding high usage. It gives numerous avenues to interpret data structures.

Robust Support

SQL is capable of handling a large number of records and manage several transactions all under one roof. So, SQL gives outstanding support to the structures and makes them durable.

What is a Primary Key in SQL?

The primary key helps you to identify records inside a table. Every table should have a single primary key but can have multiple minimal superkeys. Primary keys should contain unique values and must not have zero values. SQL issues an error message, if you update a row which would cause a duplicate primary key. So, the primary helps to reinforce data integrity and achieve unique data compilation.

Rules for applying primary keys

There are a few rules which one should follow before using primary keys in SQL, and some of these are:

  • The principal fundamental value must contain unique numbers and only one single record within the table. If the rows can’t be uniquely identified, it can result in creating error values or duplicate rows. It can also result in cross tabbing behavior or analytical engine failure.
  • The values should not be null because these values will be deleted during the result. A table when joined to another one doesn’t identify null values because it is impossible to join null values to other parts of the table
  • The primary key value should not change under any circumstances. The value changes disrupt the whole system

Create a Table with a primary key

Create a table for customers

Customer IdCustomer namePhone Number

Customer id int not a null primary key, customer name varchar(255) not null, phone number, int

Applying the key on multiple columns

Create a table for customer

Customer id int not null

Customer name varchar(255) not null,

Phonenumber int,

Constraint PK_customer primary key (customer id, customer name);

Customer IdCustomer namePhone Number

Column 1 and 2 are the primary keys.

Create Primary Key (Alter table statement)

You can use the Alter Table statement to and create a primary key if your table already exists if you want to add a primary key later.


The Syntax to create the Alter Table in SQL is:
Alter table table_name
Add constraint constraint_name
Primary key (column1, column2,….column_n)

Table names are the ones that add a primary key. Constraint name is the name of the primary key. The columns are the ones that make up the primary key functions.

Drop Primary Key

The syntax of the table is as follows:

Alter table table_name

Drop primary key;

So, if you wish to drop a table name, you can use this primary key.

Let’s take an example of this:

Alter table suppliers
Drop primary key

This decreases the primary key on the supplier’s table. There is no need to write the name of the primary key, as there can only be one primary key.

Some features of primary keys

There are some basic features of the primary keys:

  • The primary should be numeric or dates, and you should refrain from using text data
  • Primary keys function better when you use short compact data structures
  • Compound keys make the SQL complex, and so, your core should contain the fewest columns
  • The primary keys should not be based on real-world data because it would be necessary to change it at some point. You should not integrate your non-key columns with your key columns.

You have gained a good knowledge of the primary keys and its use in creating table structures. If the above situations are not met, you might need to use surrogate keys for creating the database. Primary keys are one of the essential parts of SQL and offer the fastest method of searching for data searches within the tables.

Related Blogs

  1. SQL Joins
  2. Schema in SQL
  3. Decode in SQL
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