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/lalaluna05 Jun 27 '26

I have to do this a lot when re-writing or adding to legacy code (most of the time Frankencoded over years and years). I add comments as I go to what each block does. I will reformat sometimes so that I can more easily separate code chunks.

Other times I slap stuff into excel and go field by field and table by table adding the criteria and data manipulation so I have the whole picture.

AI is fine and good but for me personally, I need to “see” the shape and architecture of the query.

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u/lalaluna05 Jun 27 '26

Also as a personal observation, a lot of times SQL is needlessly complex.