Explain MySQL 8.0's new features: CTEs, Window Functions, and JSON improvements.

CTEs (Common Table Expressions):
WITH RECURSIVE cte AS (
  SELECT 1 as n UNION ALL
  SELECT n+1 FROM cte WHERE n<10
) SELECT * FROM cte;

Window Functions:
SELECT name, salary, ROW_NUMBER() OVER (ORDER BY salary DESC) as rank FROM employees;

JSON improvements:
• JSON_TABLE() function
• Multi-valued indexes
• JSON aggregation functions