Mastering SQL Constraints: Primary Key, Unique Key, Not Null, and CHECK Explained!

In this video, we dive into the essential SQL constraints that ensure data integrity and consistency in your databases. Learn how to use PRIMARY KEY, UNIQUE, NOT NULL, and CHECK constraints to manage your data effectively. We walk through practical examples with hospital and doctor records to show you how these constraints work in action. Whether you're a beginner or looking to brush up on your SQL skills, this tutorial is perfect for you! -- CONSTRAINTS PRIMARY KEY -- Make sure that the column does not have null values and is always having unique records NOT NULL -- Define a column as not null if you never want to have null values in it. CHECK -- Validates with the given list of values UNIQUE -- Avoid duplicate values. But it allows NULL values. drop table if exists hospitals; create table hospitals ( hospital_code int , hospital_name varchar(50) , location varchar(200), contact_no bigint, constraint pk_hospitals primary key (hospital_code,hospital_name) ); insert into hospitals values (1, 'Fortis Hospital', 'Bangalore', 9900099000); insert into hospitals values (2, 'Manipal Hospital', 'Manipal', 9900099222); insert into hospitals values (3, 'Apollo Hospital', 'Mumbai', 9900099333); insert into hospitals values (4, 'St. Francis Hospital', 'New York', 17194440001); insert into hospitals values (4, 'Duke Hospital', 'New York', 17194440022); select * from hospitals; drop table if exists Doctors; create table Doctors ( id varchar(15) primary key, first_name varchar(50) not null , last_name varchar(50) not null, specilization varchar(200), gender bigint, dob date, salary int, hospital_id int ); ALTER TABLE DOCTORS alter column gender varchar(10); insert into Doctors values ('D1', 'Ragav', 'Jain', 'Cardiology', 'Male', convert(date,'01-01-1980',105), 250000, 4); insert into Doctors values ('D2', 'Priyanka', 'Verma', 'Physician', 'female', convert(date,'01-01-1995',105), 350000, 3); insert into Doctors values ('D3', 'Sheetal', 'Shetty', 'Neurology', 'F', convert(date,'01-01-1980',105), 200000, 3); insert into Doctors values ('D4', 'David', 'Smith', 'Psyatry', 'M', convert(date,'01-01-1970',105), 150000, 1); insert into Doctors values ('D5', 'James', 'Dias', 'Oncology', 'm', convert(date,'01-01-1985',105), 150000, 2); insert into Doctors values ('D6', 'Ali', 'Abdal', 'Dermatology', 'M', convert(date,'01-01-1990',105), 250000, 5); insert into Doctors values ('D6', null, null, 'Dermatology', 'M', convert(date,'01-01-1990',105), 250000, 5); drop table if exists Patients; create table Patients ( id varchar(15) unique, first_name varchar(50), last_name varchar(50), gender varchar(10) check (gender in ('M', 'F', 'Male', 'Female')), dob date, phone_no bigint, blood_group varchar(15) ); select * from patients; insert into Patients values ('P1', 'Vishva', 'Kumar', 'Male', convert(date,'10-05-1990',105), 9990099900, 'A+'); insert into Patients values ('P2', 'Steven', 'Smith', 'Male', convert(date,'10-05-1990',105), 9990099901, 'B+'); insert into Patients values ('P3', 'Ram', 'Kumar', 'Male', convert(date,'11-05-1990',105), 9990099902, 'O+'); insert into Patients values ('P4', 'Raju', 'Sharma', 'Male', convert(date,'14-05-1990',105), 9990099903, 'O-'); insert into Patients values ('P5', 'Eshal', 'Maryam', 'Female', convert(date,'10-07-1990',105), 9990099904, 'A-'); insert into Patients values ('P6', 'Reshal', 'Verma', 'F', convert(date,'10-05-1990',105), 9990099905, 'A+'); insert into Patients values ('P7', 'Rajeev', 'Verma', 'Fix', convert(date,'10-05-1990',105), 9990099905, 'A+'); Understanding SQL Foreign Keys: Building Relationships Between Tables https://youtu.be/mA_pE0Kg9K4 SQL Identity Column: Auto-Generating Unique Values for Your Tables https://youtu.be/PZVDNekwrNc SQL DML & DDL Commands Explained | Insert, Update, Delete, Truncate, Drop https://youtu.be/DSe2Gw6Z-z0 Master Basic SQL Queries & Operators | Part 1: Fetch, Filter & Count https://youtu.be/HgKW590CVSI SQL Functions and Queries: Aggregate, CAST, REPLACE, ROUND, GETDATE https://youtu.be/w1Vvj4IFYsE Mastering SQL INNER JOIN: Essential Queries & Examples https://youtu.be/NzFpLo1J5oI SQL Group By Explained with Examples | Master Aggregate Queries https://youtu.be/9nrVo0h7Z8o Mastering SQL: Group By, Having, CASE, Order By, Join, Top, and Limit https://youtu.be/sQv2y1CTJIU Introduction to SQL Normalization: 1NF (First Normal Form) - Part 1 https://youtu.be/r_dHyFqK19g Understanding SQL Normalization: 2NF (Second Normal Form) - Part 2 https://youtu.be/2ZF3NVxYIcE Mastering SQL Normalization: 3NF (Third Normal Form) Explained - Part 3 https://youtu.be/ne-0qFcP3ao Master SQL Subqueries: Scalar, Multi-Row, and Correlated Subqueries Explained https://youtu.be/twAnX7-rAAk SQL Tutorial: Remove Duplicate Data Efficiently | Common Interview Question https://youtu.be/M2lwOXk4ZfA