What is deferred name resolution in SQL Server

Let me explain deferred name resolution with an example. Consider the stored procedure shown below.

Create procedure spGetCustomers
as
Begin
Select * from Customers1
End

Customers1 table does not exist. When you execute the above SQL code, the stored procedure spGetCustomers will be successfully created without errors. But when you try to call or execute the stored procedure using Execute spGetCustomers, you will get a run time error stating Invalid object name 'Customers1'.

So, at the time of creating stored procedures, only the syntax of the sql code is checked. The objects used in the stored procedure are not checked for their existence. Only when we try to run the procedure, the existence of the objects is checked. So, the process of postponing, the checking of physical existence of the objects until runtime, is called as deffered name resolution in SQL server.

Functions in sql server does not support deferred name resolution. If you try to create an inline table valued function as shown below, we get an error stating Invalid object name 'Customers1' at the time of creation of the function itself.

Create function fnGetCustomers()
returns table
as
return Select * from Customers1

So, this proves that, stored procedures support deferred name resolution, where as functions does not. Infact, this is one of the major difference between functions and stored procedures in sql server.

Stored Procedure

Write a Stored Procedure that takes column name as a parameter and returns the result sorted by the column that is passed

Let's understand the requirement better with an example. I have an Employee table as shown below. 


I want a stored procedure that returns employee data sorted by a column, that the user is going to pass into the stored procedure as a parameter. There are 2 ways of doing this.

Option 1: Use Case Statement as shown below:
Create Proc spGetEmployeesSorted
@SortCoumn nvarchar(10)
as
Begin

Select [Id],[Name],[Gender],[Salary],[City] 
From   [Employee]
Order by Case When @SortCoumn = 'Id' Then Id End,
                Case When @SortCoumn = 'Name' Then Name End,
                Case When @SortCoumn = 'Gender' Then Gender End,
                Case When @SortCoumn = 'Salary' Then Salary End,
                Case When @SortCoumn = 'City' Then City End
End


Option 2: Use Dynamic SQL as shown below:
Create Proc spGetEmployeesSortedUsingDynamicSQL
@SortCoumn nvarchar(10)
as
Begin

Declare @DynamicQuery nvarchar(100)
Set @DynamicQuery = 'select [Id],[Name],[Gender],[Salary],[City] from [Employee] order by ' + @SortCoumn
Execute(@DynamicQuery)

End

SQL Server interview questions on string manipulation functions

The following 2 SQL Server Interview questions were asked when I attended an interview for SQL Server Developer role.

Can you list a few useful string manipulation functions in SQL Server?
LEN(), SUBSTRING(), CHARINDEX(), LEFT(), RIGHT() etc.



Then he asked me, Can you give me one example of where you have used these functions in your experience?
The following is one simple real time example, where we can use LEN(), CHARINDEX() and SUBSTRING() functions. Let us assume we have table as shown below. 


I want you to write a query to find out total number of emails, by domain. The result of the query should be as shown below.

We can use LEN(), CHARINDEX() and SUBSTRING() functions to produce the desired results. Please refer to the query below.

Select SUBSTRING(Email,CHARINDEX('@',Email)+1,(LEN(Email) - CHARINDEX('@',Email))) as EmailDomain, Count(*) as Total From TableName  Group By SUBSTRING(Email,CHARINDEX('@',Email)+1,(LEN(Email) - CHARINDEX('@',Email))) Order by Count(*) Desc

There could be even better ways of producing the same result. If you feel you have a better way of producing the same output, please share using the form below.

What are the different ways to replace NULL values in SQL Server

This interview question is not that common. My friend faced this interview question, when he attended an interview in London. My friend said we can use  COALESCE() in SQL Server. Then the interviewer said, that's very good answer, but do you know of any other way? 

Apart from using COALESCE(), there are 2 other ways to replace NULL values in SQL Server. Let's understand this with an example.

I have a Table tblEmployee, as shown in the diagram below. Some of the Employees does not have gender. All those employees who does not have Gender, must have a replacement value of 'No Gender' in your query result. Let's explore all the 3 possible options we have.


Option 1 : Replace NULL values in SQL Server using ISNULL() function.

Select Name, ISNULL(Gender,'No Gender') as Gender
From tblEmployee


Option 2 : Replace NULL values in SQL Server using CASE.

Select Name, Case  When Gender IS NULL Then 'No Gender' Else Gender End as Gender
From tblEmployee


Option 3 : Replace NULL values in SQL Server using COALESCE() function.

Select Name, Coalesce(Gender, 'No Gender') as Gender
From tblEmployee


These are the 3 options that I can think of at the moment. If you can think of any other option, please post it here.

Advantages of stored procedures

This is a very common sql server interview question. There are several advantages of using stored procedures over adhoc queries, as listed below. 1. Better Performance : Stored Procedures are compiled and their execution plan is cached and used again, when the same SP is executed again. Although adhoc queries also create and reuse plan, the plan is reused only when the query is textual match and the datatypes are matching with the previous call. Any change in the datatype or you have an extra space in the query then, a new plan is created. 2. Better Security : Applications making use of dynamically built adhoc sql queries are highly susceptible to sql injection attacks, where as Stored Procedures can avoid SQL injection attacks completely. 3. Reduced Network Traffic: Stored procedures can reduce network traffic to a very great extent when compared with adhoc sql queries. With stored procedures, you only need to send the name of the procedure between client and server. Imagine the amount of network bandwith that can be saved especially if the stored procedure contains 1000 to 2000 lines of SQL. 4. Better Maintainance and Reusability: Stored procedures can be used any where in the application. It is easier to maintain a stored procedure that is used on several pages as themodfifcations just need to be changed at one place where the stored procedure is defined. On the other hand, maintaining an adhoc sql query that's used on several pages is tedious and error prone, as we have to make modifications on each and every page. If you can think of any other advantage of using stored procedures, please contribute by submitting the form below.

Difference between Index Scan and Index Seek and Index Scan:

Index Scan scans each and every record in the index. Table Scan is where the table is processed row by row from beginning to end. If the index is a clustered index then an index scan is really a table scan. Since a scan touches every row in the table whether or not it qualifies, the cost is proportional to the total number of rows in the table. Hence, a scan is an efficient strategy only if the table is small. 

Index Seek:
Since a seek only touches rows that qualify and pages that contain these qualifying rows, the cost is proportional to the number of qualifying rows and pages rather than to the total number of rows in the table. 

Example
I have an employee table as shown in the diagram below. EmployeeId is the primary key. We have a clustered index on the employeeId column. 



Query 1 : Select * from Employee where FirstName='Ben'
Query 2 : Select * from Employee where EmployeeId=2

Query 1 will do an Index scan (Table Scan) to retrieve the record as there is no Index on the FirstName column. 
Query 2 will do an Index seek to retrieve the record as there is an Index on the EmployeeId column. 

So from this example, you should have understood that, a query will result into an index seek, only if there is an index on the table to help they query to retrieve the data.

Self Join with an example

There are 3 different types of joins available in sql server, and they are

1. Cross Join 
2. Inner Join or Join 
3. Outer Join

Outer Join is again divided into 3 types as shown below.
1. Left Outer Join or Left Join 
2. Right Outer Join or Right Join 
3. Full Outer Join or Full Join 

I strongly recomend to learn about the basics and types of joins, before reading this article. Read the articles below, before proceeding with self join.
1. Basics of Joins
2. Inner Join
3. Left Outer Join
4. Right Outer Join
5. Full Outer Join


Self join is not a different type of join. Self join means joining a table with itself. We can have an inner self join or outer self join. Let us try to understand with an example.

To set up the data for the example, use the script below to create Employee Table and populate it with some sample data. We will be usingEmployee Table to understand Self Join.

CREATE TABLE EMPLOYEE
(
[EMPLOYEEID] INT PRIMARY KEY,
[NAME] NVARCHAR(50),
[MANAGERID] INT
)
GO

INSERT INTO EMPLOYEE VALUES(101,'Mary',102)
INSERT INTO EMPLOYEE VALUES(102,'Ravi',NULL)
INSERT INTO EMPLOYEE VALUES(103,'Raj',102)
INSERT INTO EMPLOYEE VALUES(104,'Pete',103)
INSERT INTO EMPLOYEE VALUES(105,'Prasad',103)
INSERT INTO EMPLOYEE VALUES(106,'Ben',103)
GO

We use Self Join, if we have a table that references itself. For example, In the Employee Table below MANAGERID column references EMPLOYEEID column. So the table is said to referencing itself. This is the right scenario where we can use Self Join. Now I want to write a query that will give me the list of all Employee Names and their respective Manager Names. In order to achieve this I can use Self Join. In the Table below,Raj is the manager for Pete,Prasad and Ben. Ravi is the manager for Raj and Mary. Ravi does not have a manager as he is the president of the Company.

The query below is an example of Self Join. Both E1 and E2 refer to the same Employee Table. In this query we are joining the Employee Table with itself. 

SELECT E1.[NAME],E2.[NAME] AS [MANAGER NAME]
FROM EMPLOYEE E1 
INNER JOIN EMPLOYEE E2 
ON E2.EMPLOYEEID =E1.MANAGERID

If we run the above query we only get 5 rows out of the 6 rows as shown below.

Inner Self Join

This is because Ravi does not have a Manager. MANAGERID column for Ravi is NULL. If we want to get all the rows then we can use LEFT OUTER JOIN as shown below.

SELECT E1.[NAME],E2.[NAME] AS [MANAGER NAME]
FROM EMPLOYEE E1 
LEFT OUTER JOIN EMPLOYEE E2 
ON E2.EMPLOYEEID =E1.MANAGERID

If we execute the above query we get all the rows, including the row that has a null value in the MANAGERID column. The results are shown below. The MANAGERNAME for 2nd record is NULL as Ravi does not have a Manager.

Left Outer Self Join

Let us now slightly modify the above query using COALESCE as shown below. Read COALESCE function in SQL Server to understand COALESCE in a greater detail.

SELECT E1.[NAME],COALESCE(E2.[NAME],'No Manager') AS [MANAGER NAME]
FROM EMPLOYEE E1 
LEFT JOIN EMPLOYEE E2 
ON E2.EMPLOYEEID =E1.MANAGERID

If we execute the above query the output will be as shown in the image below. This is how COALESCE can be used.

Left Outer Self Join with COALESCE

Full Outer Join in SQL Server with an example

Inner Join and left join are the most commonly used joins in real time projects. It is very important that you understand the basics of joins before reading this article. Please read the articles below if you have not done so already.

1. Basics of Joins in SQL Server
2. Inner Join
3. Left Join
4. Right Join
Now, let us understand Full Outer join with an example.

Create 2 tables Company and Candidate. Use the script below to create these tables and populate them. CompanyId column in Candidate Table is a foreign key referencing CompanyId in Company Table.

CREATE TABLE Company
(
    CompanyId TinyInt Identity Primary Key,
    CompanyName Nvarchar(50) NULL
)
GO

INSERT Company VALUES('DELL')
INSERT Company VALUES('HP')
INSERT Company VALUES('IBM')
INSERT Company VALUES('Microsoft')
GO

CREATE TABLE Candidate
(
    CandidateId tinyint identity primary key,
    FullName nvarchar(50) NULL,
    CompanyId tinyint REFERENCES Company(CompanyId)
)
GO

INSERT Candidate VALUES('Ron',1)
INSERT Candidate VALUES('Pete',2)
INSERT Candidate VALUES('Steve',3)
INSERT Candidate VALUES('Steve',NULL)
INSERT Candidate VALUES('Ravi',1)
INSERT Candidate VALUES('Raj',3)
INSERT Candidate VALUES('Kiran',NULL)
GO



If you want to select all the rows from the LEFT Table ( In our example Candidate Table ) plus all the rows from the RIGHT table ( In our exampleCompany Table ) , then we use FULL OUTER JOIN. A query involving a FULL OUTER JOIN for the Candidate and Company Table is shown below.

SELECT Cand.CandidateId, Cand.FullName, Cand.CompanyId, Comp.CompanyId, Comp.CompanyName
FROM Candidate Cand
FULL OUTER JOIN Company Comp
ON Cand.CompanyId = Comp.CompanyId

If we run the above query the output will be as shown in below. If you look at the out put, we now got 8 rows. All the rows from the Candidate Table and all the rows from the Company Table.

Full Outer Join Result

Instead of using FULL OUTER JOIN keyword we can just use FULL JOIN keyword as shown below. FULL OUTER JOIN or FULL JOIN means the same.

SELECT Cand.CandidateId, Cand.FullName, Cand.CompanyId, Comp.CompanyId, Comp.CompanyName
FROM Candidate Cand
FULL JOIN Company Comp
ON Cand.CompanyId = Comp.CompanyId

If you can think of any other sql server interview questions please post them as comments, so they will be useful to other users like you. This will be a great help from your side to improve this site.

Right Outer Join with an example

Inner Join and left join are the most commonly used joins in real time projects. 

Now, let us understand Right Outer join with an example.

Create 2 tables Company and Candidate. Use the script below to create these tables and populate them. CompanyId column in Candidate Table is a foreign key referencing CompanyId in Company Table.

CREATE TABLE Company
(
    CompanyId TinyInt Identity Primary Key,
    CompanyName Nvarchar(50) NULL
)
GO

INSERT Company VALUES('DELL')
INSERT Company VALUES('HP')
INSERT Company VALUES('IBM')
INSERT Company VALUES('Microsoft')
GO

CREATE TABLE Candidate
(
    CandidateId tinyint identity primary key,
    FullName nvarchar(50) NULL,
    CompanyId tinyint REFERENCES Company(CompanyId)
)
GO

INSERT Candidate VALUES('Ron',1)
INSERT Candidate VALUES('Pete',2)
INSERT Candidate VALUES('Steve',3)
INSERT Candidate VALUES('Steve',NULL)
INSERT Candidate VALUES('Ravi',1)
INSERT Candidate VALUES('Raj',3)
INSERT Candidate VALUES('Kiran',NULL)
GO



If you want to select all the rows from the LEFT Table ( In our example Candidate Table) that have non null foreign key values plus all the rows from the RIGHT table ( In our example Company Table) including the rows that are not referenced in the LEFT Table, then we use RIGHT OUTER JOIN. A query involving a RIGHT OUTER JOIN for the Candidate and Company Table is shown below.

SELECT Cand.CandidateId, Cand.FullName, Cand.CompanyId, Comp.CompanyId, Comp.CompanyName
FROM Candidate Cand
RIGHT OUTER JOIN Company Comp
ON Cand.CompanyId = Comp.CompanyId

If we run the above query the output will be as shown in below. If you look at the out put, we now got 6 rows. All the rows from the Candidate Table that has non null foreign key value plus all the rows from the Company Table including the row that is not referenced in the Candidate Table.

Right Outer Join Results

Instead of using RIGHT OUTER JOIN keyword we can just use RIGHT JOIN keyword as shown below. RIGHT OUTER JOIN or RIGHT JOIN means the same.

SELECT Cand.CandidateId, Cand.FullName, Cand.CompanyId, Comp.CompanyId, Comp.CompanyName
FROM Candidate Cand
RIGHT JOIN Company Comp
ON Cand.CompanyId = Comp.CompanyId

If you can think of any other sql server interview questions please post them as comments, so they will be useful to other users like you. This will be a great help from your side to improve this site.

Left Join with an example

Inner Join and left join are the most commonly used joins in real time projects. Now, let us understand Left join with an example.

Create 2 tables Company and Candidate. Use the script below to create these tables and populate them. CompanyId column in Candidate Table is a foreign key referencing CompanyId in Company Table.

CREATE TABLE Company
(
    CompanyId TinyInt Identity Primary Key,
    CompanyName Nvarchar(50) NULL
)
GO

INSERT Company VALUES('DELL')
INSERT Company VALUES('HP')
INSERT Company VALUES('IBM')
INSERT Company VALUES('Microsoft')
GO

CREATE TABLE Candidate
(
    CandidateId tinyint identity primary key,
    FullName nvarchar(50) NULL,
    CompanyId tinyint REFERENCES Company(CompanyId)
)
GO

INSERT Candidate VALUES('Ron',1)
INSERT Candidate VALUES('Pete',2)
INSERT Candidate VALUES('Steve',3)
INSERT Candidate VALUES('Steve',NULL)
INSERT Candidate VALUES('Ravi',1)
INSERT Candidate VALUES('Raj',3)
INSERT Candidate VALUES('Kiran',NULL)
GO



If you want to select all the rows from the LEFT table ( In our example Candidate Table ) including the rows that have a null foreign key value ( CompanyId in Candidate Table is the foreign key ) then we use LEFT OUTER JOIN. A query involving a LEFT OUTER JOIN for the Candidate and Company Table is shown below.

SELECT Cand.CandidateId, Cand.FullName, Cand.CompanyId, Comp.CompanyId, Comp.CompanyName
FROM Candidate Cand
LEFT OUTER JOIN Company Comp
ON Cand.CompanyId = Comp.CompanyId

If we run the above query the output will be as shown in below. If you look at the out put, we now got all 7 rows ( All the rows from the Candidate Table ) including the row that has a null value for the CompanyId column in the Candidate Table. So, LEFT OUTER JOIN would get all the rows from theLEFT Table including the rows that has null foreign key value.

Left Join Result

Instead of using LEFT OUTER JOIN keyword we can just use LEFT JOIN keyword as shown below. LEFT OUTER JOIN or LEFT JOIN means the same.

SELECT Cand.CandidateId, Cand.FullName, Cand.CompanyId, Comp.CompanyId, Comp.CompanyName
FROM Candidate Cand
LEFT JOIN Company Comp
ON Cand.CompanyId = Comp.CompanyId

If you can think of any other sql server interview questions please post them as comments, so they will be useful to other users like you. This will be a great help from your side to improve this site.

Inner Join with an example

Inner Join and left join are the most commonly used joins in real time projects. We will talk about left join in a later article. Now, let us understandInner join with an example.

Create 2 tables Company and Candidate. Use the script below to create these tables and populate them. CompanyId column in Candidate Table is a foreign key referencing CompanyId in Company Table.

CREATE TABLE Company
(
    CompanyId TinyInt Identity Primary Key,
    CompanyName Nvarchar(50) NULL
)
GO

INSERT Company VALUES('DELL')
INSERT Company VALUES('HP')
INSERT Company VALUES('IBM')
INSERT Company VALUES('Microsoft')
GO

CREATE TABLE Candidate
(
    CandidateId tinyint identity primary key,
    FullName nvarchar(50) NULL,
    CompanyId tinyint REFERENCES Company(CompanyId)
)
GO

INSERT Candidate VALUES('Ron',1)
INSERT Candidate VALUES('Pete',2)
INSERT Candidate VALUES('Steve',3)
INSERT Candidate VALUES('Steve',NULL)
INSERT Candidate VALUES('Ravi',1)
INSERT Candidate VALUES('Raj',3)
INSERT Candidate VALUES('Kiran',NULL)
GO



If you want to select all the rows from the LEFT table(In our example Candidate Table) that have a non null foreign key value(CompanyId inCandidate Table is the foreign key) then we use INNER JOIN. A query involving an INNER JOIN for the Candidate and Company Table is shown below. 

SELECT Cand.CandidateId, Cand.FullName, Cand.CompanyId, Comp.CompanyId, Comp.CompanyName
FROM Candidate Cand
INNER JOIN Company Comp
ON Cand.CompanyId = Comp.CompanyId

If we run the above query the output will be as shown in the image below. If you look at the out put, we only got 5 rows. We did not get the 2 rows which has NULL value in the CompanyId column. So an INNER JOIN would get all the rows from the LEFT Table that has non null foreign key value.

Inner Join Result

Instead of using INNER JOIN keyword we can just use JOIN keyword as shown below. JOIN or INNER JOIN means the same.

SELECT Cand.CandidateId, Cand.FullName, Cand.CompanyId, Comp.CompanyId, Comp.CompanyName
FROM Candidate Cand
JOIN Company Comp
ON Cand.CompanyId = Comp.CompanyId

If you can think of any other sql server interview questions please post them as comments, so they will be useful to other users like you. This will be a great help from your side to improve this site.

SQL Server Interview Questions on Views - Part 2

Can you create a view based on other views?
Yes, you can create a view based on other views. Usually we create views based on tables, but it also possible to create views based on views.

Can you update views?
Yes, views can be updated. However, updating a view that is based on multiple tables, may not update the underlying tables correctly. To correctly update a view that is based on multiple tables you can make use INSTEAD OF triggers in SQL Server. 



What are indexed views?
Or
What are materialized views?

A view is a virtual table, it does not contain any physical data. A view is nothing more than compiled SQL query. Every time, we issue a select query against a view, we actually get the data from the underlying base tables and not from the view, as the view itself does not contain any data.

When you create an index on a view, the data gets physically stored in the view. So, when we issue a select query against an indexed view, the data is retrieved from the index without having to go to the underlying table, which will make the select statement to work slightly faster. However, the disadvantage is, INSERT, UPDATE and DELETE operations will become a little slow, because every time you insert or delete a row from the underlying table, the view index needs to be updated. Inshort, DML operations will have negative impact on performance.

Oracle refers to indexed views as materialized views.

Only the views created with schema binding, can have an Index. Simply adding WITH SCHEMABINDING to the end of the CREATE VIEW statement will accomplish this. However, the effect is that any changes to the underlying tables which will impact the view are not allowed. Since the indexed view is stored physically, any schema changes would impact the schema of the stored results set. Therefore, SQL Server requires that schema binding be used to prevent the view's schema (and therefore the underlying tables) from changing.

The first index for a view must be a UNIQUE CLUSTERED INDEX, after which, it's possible to create non-clustered indexes against the view.

Indexed Views are heavily used in data warehouses and reporting databases that are not highly transactional.

What are the limitations of a View?
1. You cannot pass parameters to a view.

2. Rules and Defaults cannot be associated with views.

3. The ORDER BY clause is invalid in views unless TOP or FOR XML is also specified.

4. Views cannot be based on temporary tables.

If you can think of any other interview questions on views please post them as comments, so they will be useful to other users like you.

SQL Server Interview Questions on Views - Part 1

What is a View in SQL Server?
You can think of a view either as a compiled sql query or a virtual table. As a view represents a virtual table, it does not physically store any data. When you query a view, you actually retrieve the data from the underlying base tables.

What are the advantages of using views?
Or 
When do you usually use views?
1. Views can be used to implement row level and column level security.

Example 1: Consider the tblEmployee table below. I don't want some of the users to have access to the salary column, but they should still be able to access ID, NAME and DEPT columns. If I grant access to the table, the users will be able to see all the columns. So, to achieve this, I can create a view as shown in Listing 1 below. Now, grant access to the view and not the table. So using views we can provide column level security.

tblEmployee Listing 1 Create View      vWEmployee As Select               ID, Name, Dept From                 tblEmployee

Example 2: Let us say, we have a few users who should be able to access only IT employee details and not any other dept. To do this, I can create a view as shown in Listing 2 below. Now, grant access only to the view and not the table. So using views we can provide row level security as well.

Listing 2
Create View     vWITEmployees
As
Select              ID, Name, Dept
From                tblEmployee
Where              Dept = 'IT'

2. Simplify the database schema to the users. You can create a view based on multiple tables which join columns from all these multiple tables so that they look like a single table.

3. Views can be used to present aggregated and summarized data.

Example 1: Consider the tblEmployee table above. I want to aggregate the data as shown in the image below. To do this I can create a view as shown in Listing 3. Now, you can simply issue a select query against the view rather than writing a complex query every time you want to retrieve the aggregated data.

Listing 3 Select        Dept, Count(*) As Total From          tblEmployee Group By   Dept If you can think of any other advantages of using views please post them as comments, so they will be useful to other users like you.

SQL Server Interview Questions on triggers

What is a Trigger in SQL Server?
A Trigger is a database object that is attached to a table. In many aspects it is similar to a stored procedure. As a matter of fact, triggers are often referred to as a "special kind of stored procedure." The main difference between a trigger and a stored procedure is that the former is attached to a table and is only fired when an INSERT, UPDATE or DELETE occurs.

What are the two types of Triggers in SQL Server?
1. After Triggers : Fired after Insert, Update and Delete operations on a table.
2. Instead of Triggers: Fired instead of Insert, Update and Delete operations on a table.

What are the special tables used by Triggers in SQL Server?
Triggers make use of two special tables called inserted and deleted. The inserted table contains the data referenced in an INSERT before it is actually committed to the database. The deleted table contains the data in the underlying table referenced in a DELETE before it is actually removed from the database. When an UPDATE is issued both tables are used. More specifically, the new data referenced in the UPDATE statement is contained in inserted table and the data that is being updated is contained in deleted table.

Give a real time example for triggers usage?
It is recomended to avoid triggers in a real time environment. There is one scenario I can think of why you may want to use triggers in a real time environment. Let us use an example to understand this.



I have 2 tables, tblPerson and tblGender as shown below. GenderId is the foriegn key in tblPerson table.

Now create a view based on the above 2 tables as shown below.

Select * from vWPersons will give us the result as shown below.

Now update the view the following query. This will change the Gender Text to Female in tblGender table for Id = 1. This is not what we have expected.

Update tblGender Set Gender='Female' where Id=1

The base tables are updated incorrectly. So, Select * from vWPersons will give us the result as shown below.

To update the base tables correctly, you can create an INSTEAD OF trigger on the view as shown below.

Now run the query below which will update the underlying base tables correctly.
Update vWPersons Set Gender='Female' Where Id=1

Select * from vWPersons, will show the correct result set as shown below. The INSTEAD OF trigger has correctly updated the GenderId in tblPerson table.
So, Instead of triggers can be used to facilitate updating Views that are based on multiple base tables.