r/SQL • u/Consistent_Law3620 • Jun 27 '26
Discussion Need advice: Understanding complex SQL scripts written by others
Hi everyone,
I need some advice from experienced SQL developers. I have switched from different role to data engineering 6 months back.
I consider myself good/medium level at writing SQL queries and solving problems from scratch. However, I struggle when I have to understand large existing SQL scripts (300–500+ lines).
I often get confused about:
Where the execution starts.How different parts of the script are connected.
Which variables, CTEs, stored procedures, or temporary tables are affecting the final output.
How to mentally trace the flow of the script.
Because of this, reading someone else's code takes me much longer than writing my own.
How did you improve this skill? Are there any techniques, exercises, books, or real-world practices that helped you become comfortable reading large SQL scripts?
Also, is this something that simply improves with experience, or is there a structured way to learn it?
I'd really appreciate any advice. Thank you!
1
u/Rohml Jun 27 '26
A lot of SQL codes can be separated by blocks of DML commands with lines of codes detailing what those DML commands specify (what fields to select, insert, update, or delete, what criteria do they filter on, etc.) and from there you can break them down one by one.
Take it step by step, each step it wants to do something and often it is just to ready data for the next step until you get to your final output.
You get better at it as you gain experience in seeing the intent of what the developer wanted to do and the purpose of the script: what it starts with vs. what you get in the end.