Quick Interview Questions on LINQ FAQ:

10 Most Asked LINQ Interview Questions and Answers for 2026

This article has top 10 linq interview questions and answers.for example,how to write linq queries,advantages of using linq,difference between select and selectmany,difference between deferredexecution and immediateexecution,remove duplicates in linq.

1. What is LINQ?

Answer:
LINQ is Language Integrated Query available from .net framework 3.5 onwards. LINQ can be operated on various datasources like ADO.NET DATASET,ENTITY FRAMEWORK,SQLSERVER DATABASE,XML DOCUMENTS,INMEMORY OBJECTS.

2. What are the advantages of using LINQ?

Answer:
Suppose our application needs data from database.we should know sql queries,ADO.NET syntax. If we need data from XML documents, we should have sufficient knowledge of XML. The application also needs data from in memory collections such as generic list like list,list etc.

3. How will you write LINQ queries?

Answer:
LINQ queries can be written in differen ways in C#: a)Normal way: var strquery= from u in users where u.gender=="Male" select u.Name; b)Fluent syntax: It uses extension methods and lambda expression var fquery= users.where(u=>u.gender=="Male").Select(u=>u.name);

4. What are the different types of LINQ?

Answer:

• LINQ to Objects
• LINQ to SQL
• LINQ to Entities (Entity Framework)
• LINQ to XML
• LINQ to DataSet

5. What is Deferred Execution in LINQ?

Answer:
LINQ query will not executed until you iterate over it.

        var data = employees.Where(e => e.Salary > 50000);
// Not executed yet
foreach(var emp in data)
{
    Console.WriteLine(emp.Name);  // Executed here
}

6. What is Immediate Execution in LINQ?

Answer:
The queries are executed immediately at the moment and results are stored in memory.
Methods like:

• ToList()
• ToArray()
• Count()
• First()

7. What is difference between First() and FirstOrDefault()?

Answer:
First() - throws exception if record not found
FirstOrDefault()- Returns default value(null)

8. What is difference between Single() and First()?

Answer:
Single() → Exactly one record must exist (throws exception if 0 or >1)
First()- Returns first match even if multiple exist

9. How to remove duplicates in LINQ?

Answer:
We begin by creating a list containing some duplicates:

List listWithDuplicates = new List() { 1, 2, 3, 4, 1, 2, 3, 4 };
          listWithDuplicates.Distinct().ToList();

10. What is the difference between Select and SelectMany?

Answer:
Select → Projects each element
SelectMany → Flattens collections
Let us consider scenario like each student has many subjects.we need to flatten subjects only.

            public class Student
{
    public string Name { get; set; }
    public List Subjects { get; set; }
}
            var students = new List
{
    new Student { Name = "John", Subjects = new List { "Math", "Science" } },
    new Student { Name = "Sara", Subjects = new List { "English", "History" } }
};

SELECT LIST NOT FLATTENED
var result = students.Select(s => s.Subjects);
OUTPUT RETURNS 2 ROWS:
[ ["Math", "Science"], ["English", "History"] ]
Using SelectMany (Flattened)
var result = students.SelectMany(s => s.Subjects);
OUTPUT RETURNS 1 ROW.
["Math", "Science", "English", "History"]
NOW IT BECOMES SINGLE FLAT LIST.