Answers for "primary key and unique key"

SQL
5

unique vs primary key

What is the difference between UNIQUE and PRIMARY KEY constraints? 
There should be only one PRIMARY KEY 
in a table whereas there can be
any number of UNIQUE Keys.
PRIMARY KEY doesn’t allow NULL
values whereas Unique key allows NULL values.
Posted by: Guest on December-23-2020
0

unique key

CREATE TABLE students  
(  
S_Id int NOT NULL,  
LastName varchar (255) NOT NULL,  
FirstName varchar (255),  
City varchar (255),  
UNIQUE (S_Id)  
)
Posted by: Guest on October-07-2020
1

difference between unique vs primary key in sql

What is the difference between UNIQUE and PRIMARY KEY constraints? 
There should be only one PRIMARY KEY 
in a table whereas there can be
any number of UNIQUE Keys.
PRIMARY KEY doesn’t allow NULL
values whereas Unique key allows NULL values.
Posted by: Guest on December-23-2020
0

unique key

ALTER TABLE students  
ADD UNIQUE (S_Id)
Posted by: Guest on October-07-2020

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