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Ace Your SQL Interview: 800+ Questions & Answers Guide

SQL is a must-have skill for database professionals. Whether you're a fresher or an experienced developer, mastering SQL queries can help you crack technical interviews. This guide covers essential SQL topics based on an 800+ SQL Interview Questions & Answers PDF.

1. SQL Basics (0-1 Year Experience)

• Retrieve all records:

  SELECT * FROM EmployeeDetail;
  

• Fetch specific columns:

  SELECT FirstName FROM EmployeeDetail;
  

• Filter records (FirstName starts with 'A'):

  SELECT * FROM EmployeeDetail WHERE FirstName LIKE 'A%';
  

• Count total employees:

  SELECT COUNT(*) FROM EmployeeDetail;
  

2. Intermediate SQL (1-3 Years Experience)

• Get employees and their projects:

  SELECT FirstName, ProjectName  
  FROM EmployeeDetail E  
  INNER JOIN ProjectDetail P ON E.EmployeeID = P.EmployeeDetailID;
  

• Find total salary by department:

  SELECT Department, SUM(Salary) AS TotalSalary  
  FROM EmployeeDetail  
  GROUP BY Department;
  

• Find duplicate names:

  SELECT FirstName, COUNT(*)  
  FROM EmployeeDetail  
  GROUP BY FirstName  
  HAVING COUNT(*) > 1;
  

3. Advanced SQL (3+ Years Experience)

• Find the second-highest salary:

  SELECT MAX(Salary)  
  FROM EmployeeDetail  
  WHERE Salary < (SELECT MAX(Salary) FROM EmployeeDetail);
  

• Find employees who joined in 2023:

  SELECT * FROM EmployeeDetail WHERE YEAR(JoiningDate) = 2023;
  

• Optimize query performance with indexes:

  CREATE INDEX idx_employee ON EmployeeDetail(FirstName);
  

4. SQL Server 2016+ Features for Interviews

• JSON Support:

  SELECT * FROM OpenJson(@jsonVariable);
  

• Temporal Tables (Tracking Changes Over Time):

  CREATE TABLE EmployeeHistory (  
      EmployeeID INT PRIMARY KEY,  
      Name VARCHAR(100),  
      ValidFrom DATETIME2 GENERATED ALWAYS AS ROW START,  
      ValidTo DATETIME2 GENERATED ALWAYS AS ROW END,  
      PERIOD FOR SYSTEM_TIME (ValidFrom, ValidTo)  
  ) WITH (SYSTEM_VERSIONING = ON);
  

Final Tips

✅ Master SQL fundamentals & Joins.
✅ Optimize queries with indexing.
✅ Stay updated with SQL Server features.

📌 Keep practicing! What’s the trickiest SQL query you've faced? Drop it in the comments! 🚀

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