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الكل سهل متوسط صعب
Write query for Nth Highest Salary in SQL صعب 
SELECT DISTINCT Salary
FROM Employees e1
WHERE N-1 = (
   SELECT COUNT(DISTINCT Salary)
   FROM Employees e2
   WHERE e2.Salary > e1.Salary
);
Extended scenario: If multiple employees have same salary - write using Dense_Rank() صعب 
SELECT *
FROM (
   SELECT Name, Salary, DENSE_RANK() OVER (ORDER BY Salary DESC) AS rnk
   FROM Employees
) t
WHERE rnk = N;
Explain the difference between Subquery and Correlated Subquery صعب
  • Subquery: Runs once, result passed to outer query.
  • Correlated Subquery: Runs for each row of outer query.
What is indexed view? صعب

An Indexed View is a view with a unique clustered index.

It materializes results, improving performance on complex queries.

How to implement Partitioning in SQL? صعب

Partitioning splits large tables into smaller, manageable parts.

Types:

  • Range
  • List
  • Hash
  • Composite
What is a Deadlock in SQL? How can you prevent it? صعب

A Deadlock occurs when two transactions wait on each other's locks.

Prevention:

  • Keep transactions short.
  • Access objects in same order.
  • Use proper indexing.
Write steps/queries for SQL Performance tuning صعب

Steps for SQL Performance Tuning:

  • Check execution plans.
  • Add proper indexes.
  • Avoid cursors, prefer set-based operations.
  • Use appropriate JOINs.
  • Optimize queries & schema.
What types of caching are available in .NET? (Related to SQL data) صعب
  • In-Memory Cache: Using IMemoryCache.
  • Distributed Cache: Using IDistributedCache (e.g., Redis, SQL Server).
  • Output Caching: For web responses.
  • EF Core Caching: Query results caching via 3rd-party libraries.