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Primary key in SqlServer


In this blog I will explain some examples that how to work with primary keys in sql server. Here in following examples I will show you that how to create primary key, how to create primary key using alter statement and how to drop primary key using alter statement.

--This is a demonstration of primary key in Sql server.

--Firstly we needs to create a table in which we can apply this demonstration.

--Creating a primary key on column label.

create table Employee

(

     EmpId varchar(5) not null constraint pk1 primary key,

     EmpRefNo varchar(10) not null,

     EmpName varchar(50) not null,

     EmpUId varchar(15) not null,

     EmpPanNo varchar(20) null

)

--Creating primary key on table label.

create table Employee

(

     EmpId varchar(5) not null,

     EmpRefNo varchar(10) not null,

     EmpName varchar(50) not null,

     EmpUId varchar(15) not null,

     EmpPanNo varchar(20) null,

     constraint pk1 primary key(EmpId)

)

--Creating primary key on multiple columns.

--When we create primary key on more than one column then

--This key is also known as composite key.

create table Employee

(

     EmpId varchar(5) not null,

     EmpRefNo varchar(10) not null,

     EmpName varchar(50) not null,

     EmpUId varchar(15) not null,

     EmpPanNo varchar(20) null,

     constraint pk1 primary key(EmpId,EmpUId)

)

--Creating primary key using alter staement.

--When we create primary key using alter statement

--Then we have to make sure that column have "not null"

--attributes and if it don't have "not null"

--attributes then we needs to assign "not null"

--attribute first using alter statement then we

--create primary key on that.

--Statements to create Employee table.

create table Employee

(

     EmpId varchar(5) not null,

     EmpRefNo varchar(10) not null,

     EmpName varchar(50) not null,

     EmpUId varchar(15) not null,

     EmpPanNo varchar(20) null,

)

--Statements to create primary key using alter statement.

alter table Employee

add constraint pk1 primary key(EmpId)

--Statements to drop primary key using alter statement.

alter table Employee

drop constraint pk1

Thanks.


Thanks

By Samuel Fernandes on   22 days ago

It was really helpful to read this post.


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