SQL Server Functions Interview Questions and Answers

SQL Server Functions Interview Questions and Answers

In this article, I am going to discuss the most frequently asked SQL Server Functions Interview Questions and Answers. Please read our previous article where we discussed the most frequently asked SQL Server Views Interview Questions and Answers. As part of this article, we are going to discuss the following SQL Server Functions Interview Questions with answers.

  1. What is a function in SQL Server?
  2. Types of User-Defined Functions in SQL Server
  3. What is a scalar function in SQL Server?
  4. What is a table-valued function?
  5. Where can we use the Inline Table-Valued function?
  6. What is Inline table-valued functions?
  7. What are Multi-Statement Table-Valued Functions in SQL Server?
  8. Differences between Inline Table-Valued functions and Multi-statement Table-Valued functions.
  9. What are the differences between functions and procedures in SQL Server?
What is a function in SQL Server?

A function is a database object in SQL Server. Basically, it is a set of SQL statements that accept only input parameters, perform actions and return the result. The function can return only a single value or a table. We can’t use the function to Insert, Update and Delete records in the database table(s). 

  1. It is also a subprogram like a stored procedure that is defined for performing an action such as complex calculation and returns result of the action as a value.
  2. These functions are created by the user or programmer.
  3. Functions are taking some parameters, do some processing and returning some results back

For example Select SQUARE(3) Output: 9

Some functions also do not take any parameters. For Example: Select GETDATE()

So, we can say that a function can have the parameter that is optional but a function should return a value that is mandatory.

Types of User-Defined Functions in SQL Server:

In SQL Server, there are 3 types of User-Defined Functions

  1. Scalar functions
  2. Inline table-valued functions
  3. Multi-statement table-valued functions
What is a scalar function in SQL Server?

The functions which return a single value are known as scalar value function. The Scalar functions may or may not have parameters, but always return a single (scalar) value. The returned value can be of any data type, except text, ntext, image, cursor, and timestamp.

To create a function, we use the following syntax:

SQL Server Functions Interview Questions and Answers
What is a table-valued function?

In this case, we can return a table as an output from the function. These are again of two types

  1. Inline Table-valued Function
  2. Multi-statement table value function
Where can we use the Inline Table-Valued function?

The Inline Table-Valued functions can be used to achieve the functionality of parameterized views. The table returned by the table-valued function can also be used in joins with other tables.

What is Inline table-valued functions?

In this case, the body of the function will have only a single select statement prepared with the “RETURN” statement. The syntax for creating a table value function

CREATE/ALTER FUNCTION <FUNCTION NAME>(@<VARIABLE NAME><DATA TYPE> [SIZE])
RETURNS TABLE
AS
RETURN <SELECT STATEMENT>
  1. We specify the Table as the return type instead of any scalar data type.
  2. The function body is not closed between BEGIN and END block
  3. The structure of the table that gets returned is determined by the select statement within the function.
What are Multi-Statement Table-Valued Functions in SQL Server?

This is the same as the inline table-valued function which can return a table as an output but here the body can contain more than one statement and also the structure of the table being returned can be defined. The Syntax is given below.

CREATE/ALTER  FUNCTION <FUNCTIONNAME> (@<PARAM><DATATYPE> [SIZE].....)
RETURNS @<TABLE VAR> TABLE (<COLUMN DEFINITIONS>)
[WITH <FUNCTION ATTRIBUTES>]
AS
BEGIN
    <FUNCTION BODY>
    RETURN
END

Note: In case of a multi-statement table-valued function we need to define our own structure to the table being return.

Differences between Inline Table-Valued functions and Multi-statement Table-Valued functions

In an Inline Table-Valued function, the RETURNS clause cannot contain the structure of the table, the function returns. Whereas, with the multi-statement table-valued function, we specify the structure of the table that gets returned

Inline Table-Valued function cannot have BEGIN and END block as it returns a single select statement, whereas the multi-statement function can have the begin and end block as it contains more than one select statement.

Inline Table-valued functions are better for performance than multi-statement table-valued functions. If the given task, can be achieved using an inline table-valued function, always prefer to use them, over multi-statement table-valued functions.

It’s possible to update the underlying table, using an inline table-valued function, but not possible using a multi-statement table-valued function.

Reason for improved performance of an inline table-valued function:

Internally, SQL Server treats an inline table-valued function much like it would a view and treats a multi-statement table-valued function similar to how it would a stored procedure.

What are the differences between functions and procedures in SQL Server?

Stored Procedures are pre-compiled objects which are compiled for the first time and its compiled format is saved which executes (compiled code) whenever it is called. But Function is compiled and executed every time when it is called. 

BASIC DIFFERENCE

  1. The function must return a value but in Stored Procedure, it is optional (Procedure can return zero or n values). 
  2. Functions can have only input parameters whereas Procedures can have input/output parameters.
  3. A Function can be called from Procedure whereas Procedures cannot be called from Function
  4. From a procedure, we can call another procedure or a function whereas from a function we can call another function but not a procedure.

ADVANCE DIFFERENCE

  1. The procedure allows SELECT as well as DML (INSERT/UPDATE/DELETE) statement in it whereas Function allows only SELECT statement in it.
  2. Procedures cannot be utilized in a SELECT statement whereas Function can be embedded in a SELECT statement.
  3. Stored Procedures cannot be used in the SQL statements anywhere in the WHERE/HAVING/SELECT section whereas Function can be.
  4. Functions that return tables can be treated as a row set. This can be used in JOINs with other tables
  5. The exception can be handled by a try-catch block in a procedure whereas try-catch block cannot be used in a Function.
  6. We can go for Transaction Management in Procedure whereas we can’t go into Function.
  7. We call a procedure using EXECUTE/ EXEC command whereas a function is called by using the SELECT command only.
  8. Stored procedures support deferred name resolution. For example, while writing a stored procedure that uses table names, for example, table1, table2, etc. but these tables do not exist in the database is allowed during the creation of the stored procedure but runtime throws error whereas functions do not support deferred name resolution.

In the next article, I am going to discuss the most frequently asked SQL Server Constraints Interview Questions and Answers. Here, in this article, I try to explain the most frequently asked SQL Server Functions Interview Questions and Answers. I hope this article will help you with your needs. I would like to have your feedback. Please post your feedback, question, or comments about this article.

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