1. Write a query to find all employees who earn more than the average salary.2. Write a query to retrieve the names of employees who work in the same department as ‘John’.3. Write a query to display the second highest salary from the Employee table.4. Write a query to find all customers who have made more than five orders.5. Write a query to count the number of orders placed by each customer.6. Write a query to retrieve the list of employees who joined in the last 6 months.7. Write a query to find the total sales amount per product.8. Write a query to list all products that have never been sold.9. Write a query to update the salary of employees based on their performance rating.10. Write a query to delete duplicate rows from a table.11. Write a query to find the second highest salary in a company without using the MAX function twice.12. Write a query to identify the top 10 customers who have not placed an order in the last year.13. Create a query to compute the year-over-year growth rate of revenue for each product category.14. Write a query to join three tables and filter the results to show only records that exist in exactly two of the tables.15. Construct a query to find the median sales amount for each region.16. Write a query to calculate the retention rate of customers over a given time period.17. Write a query to find duplicate records in a table and count the number of duplicates for each unique record.18. Create a query to find employees who have been with the company for more than 5 years but have never been promoted.

Sure, here are the SQL queries for each of your requests:

SELECT * FROM Employees
WHERE Salary > (SELECT AVG(Salary) FROM Employees);

SELECT e.Name FROM Employees e
JOIN Departments d ON e.DepartmentId = d.Id
WHERE d.Name = (SELECT DepartmentId FROM Employees WHERE Name = 'John');

SELECT MAX(Salary) FROM Employee
WHERE Salary NOT IN (SELECT MAX(Salary) FROM Employee);

SELECT CustomerId FROM Orders
GROUP BY CustomerId
HAVING COUNT(OrderId) > 5;

SELECT CustomerId, COUNT(OrderId) FROM Orders
GROUP BY CustomerId;

SELECT * FROM Employees
WHERE JoiningDate > DATE_SUB(CURDATE(), INTERVAL 6 MONTH);

SELECT ProductId, SUM(SalesAmount) FROM Sales
GROUP BY ProductId;

SELECT * FROM Products
WHERE ProductId NOT IN (SELECT DISTINCT ProductId FROM Sales);

UPDATE Employees
SET Salary = CASE 
    WHEN PerformanceRating = 'Excellent' THEN Salary * 1.1
    WHEN PerformanceRating = 'Good' THEN Salary * 1.05
    ELSE Salary
END;

DELETE FROM table
WHERE rowid NOT IN 
(SELECT MIN(rowid) FROM table GROUP BY column);

SELECT MAX(Salary) FROM Employee
WHERE Salary NOT IN (SELECT MAX(Salary) FROM Employee);

SELECT CustomerId FROM Customers
WHERE CustomerId NOT IN 
(SELECT DISTINCT CustomerId FROM Orders WHERE OrderDate > DATE_SUB(CURDATE(), INTERVAL 1 YEAR))
LIMIT 10;

SELECT ProductCategory, 
       (SUM(Revenue) - LAG(SUM(Revenue), 1) OVER (PARTITION BY ProductCategory ORDER BY Year)) / LAG(SUM(Revenue), 1) OVER (PARTITION BY ProductCategory ORDER BY Year) AS YoY_Growth
FROM Sales
GROUP BY Year, ProductCategory;

SELECT * FROM Table1
JOIN Table2 ON Table1.Id = Table2.Id
JOIN Table3 ON Table1.Id = Table3.Id
WHERE (Table1.Id IS NULL AND Table2.Id IS NOT NULL AND Table3.Id IS NOT NULL)
OR (Table1.Id IS NOT NULL AND Table2.Id IS NULL AND Table3.Id IS NOT NULL)
OR (Table1.Id IS NOT NULL AND Table2.Id IS NOT NULL AND Table3.Id IS NULL);

SELECT Region, AVG(SalesAmount) AS MedianSales
FROM (SELECT Region, SalesAmount, COUNT(*) OVER (PARTITION BY Region) AS Total, ROW_NUMBER() OVER (PARTITION BY Region ORDER BY SalesAmount) AS Rank
      FROM Sales) sub
WHERE Rank = Total / 2 OR Rank = Total / 2 + 1
GROUP BY Region;

SELECT COUNT(DISTINCT CustomerId) / (SELECT COUNT(DISTINCT CustomerId) FROM Customers WHERE JoinDate < DATE_SUB(CURDATE(), INTERVAL period YEAR)) AS RetentionRate
FROM Orders
WHERE OrderDate > DATE_SUB(CURDATE(), INTERVAL period YEAR);

SELECT column, COUNT(*) 
FROM table
GROUP BY column
HAVING COUNT(*) > 1;

SELECT * FROM Employees
WHERE JoinDate < DATE_SUB(CURDATE(), INTERVAL 5 YEAR)
AND EmployeeId NOT IN (SELECT DISTINCT EmployeeId FROM Promotions);

Please replace table, column, period, Employee, Employees, Departments, Orders, Sales, Products, Customers, Promotions with your actual table names and Salary, Name, DepartmentId, JoiningDate, PerformanceRating, ProductId, SalesAmount, CustomerId, OrderId, OrderDate, ProductCategory, Revenue, Year, Region, JoinDate, EmployeeId with your actual column names.