How to replace string in SQL Server?

Introduction: 
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Here i will give an example how to replace a substring in a string in SQL Server. 
For example you want to change domain in Employee email addresses in 'EmployeeDetails' table.

In the below example i am replacing  EmailId  from "@gmail.com" to "studentboxoffice.in" in 'EmployeeDetails' Table .

Example: 1)
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Declare @txt1 varchar(50)
set @txt1 = 'vikramreddy@gmail.com'
/* Here i am replacing @gmail.com to @studentboxoffice.in */
set @txt1 = REPLACE(@txt1, '@gmail.com', '@studentboxoffice.in')
select @txt1

Output:
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vikramreddy@studentboxoffice.in

Exmple: 2)
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You can also update employee emailid in 'EmployeeDetails' table. 

-- before update EmailID = 'vikramreddy@gmail.com'

update    EmployeeDetals 
set        EmailID = REPLACE(EmailID, '@gmail.com', '@studentboxoffice.in')
where    EmployeeCode = 3151

-- After updating EmailID = 'vikramreddy@studentboxoffice.in'