You learn to read execution plans. Because you understand logical processing, you can look at a plan and immediately identify the bottleneck—whether it’s a missing index or a poorly written OR predicate.
You cannot hack your way through relational theory. You must understand it. Whether you are aiming for a promotion, a certification, or simply the respect of your peers, buying this book (or renting it via O’Reilly Online) and working through every single exercise is the highest-leverage activity you can do for your career in data. itzik ben-gan t-sql fundamentals
Whether you are a junior data analyst struggling with GROUP BY or a senior architect designing complex reporting solutions, mastering the fundamentals of T-SQL through Itzik’s lens is a non-negotiable step toward excellence. You learn to read execution plans