unique key
CREATE TABLE students
(
S_Id int NOT NULL,
LastName varchar (255) NOT NULL,
FirstName varchar (255),
City varchar (255),
UNIQUE (S_Id)
)unique key
CREATE TABLE students
(
S_Id int NOT NULL,
LastName varchar (255) NOT NULL,
FirstName varchar (255),
City varchar (255),
UNIQUE (S_Id)
)primary key and unique 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.unique key in sql
Unique Key:
Only unique value and also can contain NULLCopyright © 2021 Codeinu
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