Sql Primary Keys

Sql Primary Keys
Nikhil
Published on 2021-08-14 16:04:15

Creating a Primary Key

CREATE TABLE Employees (
Id int NOT NULL,
PRIMARY KEY (Id),
...
);

This will create the Employees table with 'Id' as its primary key. The primary key can be used to uniquely identify the rows of a table. Only one primary key is allowed per table.

A key can also be composed by one or more fields, so called composite key, with the following syntax:

CREATE TABLE EMPLOYEE (
e1_id INT,
e2_id INT,
PRIMARY KEY (e1_id, e2_id)
)

Using Auto Increment

Many databases allow to make the primary key value automatically increment when a new key is added. This ensures that every key is different.

MySQL

CREATE TABLE Employees (
Id int NOT NULL AUTO_INCREMENT,
PRIMARY KEY (Id)
);

PostgreSQL

CREATE TABLE Employees (
Id SERIAL PRIMARY KEY
);

SQL Server

CREATE TABLE Employees (
Id int NOT NULL IDENTITY,
PRIMARY KEY (Id)
);

SQLite

CREATE TABLE Employees (
Id INTEGER PRIMARY KEY
);

ATutorialHub Related Guide

Comments (8)

Leave a Comment

Your email address will not be published. Required fields are marked*

User Comments

html tutorial comments

panduranga gupta

2021-07-05 07:03:13

good website for learning and help me a lot

html tutorial comments

raju

2021-09-25 14:58:47

The awsome website i am looking like for a long time, good work atutorialhub team keep doing

html tutorial comments

Shivani

2021-09-01 15:03:56

Learning a lot from the courses present on atutorialhub. The courses are very well explained. Great experience

html tutorial comments

Harshitha

2021-09-10 15:05:45

It is very helpful to students and easy to learn the concepts

html tutorial comments

Sowmya

2021-09-14 15:06:41

Great job Tutorials are easy to understand Please make use of it

html tutorial comments

Zain Khan

2021-09-18 15:07:23

Great content and customized courses.

html tutorial comments

Rudrakshi Bhatt

2021-09-09 15:08:10

Well structured coursed and explained really well!

html tutorial comments

Pavana Somashekar

2021-09-11 15:09:08

Good platform for beginners and learn a lot on this website