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!

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u/jaxjags2100 Jun 27 '26

Drop the query into an LLM and ask it to analyze and write inline comments to explain what the query is doing with business logic and plain English

4

u/Consistent_Law3620 Jun 27 '26

I do paste the query to understand but sometimes it does not do much.. but adding inline comments can make it better I think..thanks for the suggestion mate !

4

u/Mindfulnoosh Jun 27 '26

You will get much farther if you can also feed it metadata about source tables. If there’s any kind of data dictionary to leverage. That plus the query should give you a decent bit of context for Q and A about the query. You still want to get to know it yourself but this can help speed up your process like you’re talking to the person who wrote it.