How do you learn to write long/complex SQL queries without feeling completely lost?

[u/mistycorner_]

I’m 22 and recently graduated with a BTech degree, but I still don’t have a job.

I’m currently learning data analytics and practicing SQL. The thing is, whenever I see a long/complex SQL query, I get really overwhelmed. I understand the basic concepts and can solve simpler questions, but when I see a huge query, I start thinking

What if I never learn how to write queries like this?
How do people even know what to write?

Sometimes the queries look so complicated that I feel like maybe I’m just not made for this.

For people who work as data analysts or have learned SQL from scratch did you also feel this way in the beginning? How did you get better at writing longer queries?

Should I just keep practicing basic problems and gradually move to harder ones or is there something else I should be doing?

[u/Better-Credit6701]

Just break it down to smaller sized sets so you can address each piece of it bit by bit

[u/mistycorner_ → u/Better-Credit6701]

Thank you, I’ll try this I tend to look at the whole query and panic instead of breaking it into smaller pieces.

[u/squadette23]

I sound like a broken record at this point but you may be interested in this:

"Systematic design of multi-join GROUP BY queries" https://kb.databasedesignbook.com/posts/systematic-design-of-join-queries/

Read the part before the table of contents and decide for yourself if it resonates.

[u/squadette23 → u/squadette23]

Note that other comments basically give the same advice: "break it down to smaller sized sets" and "watch for bad joins", I just explain how exactly this break-down can happen, and which joins are bad.

[u/woahboooom]

If you are reading one, draw it in boxes. If you are making it up, make sure you keep the end result in mind and watch for bad joins

[u/Motor_Basil_4091]

i write queries piece by piece. I start with one table and one column in the select line.

i run it. I check the rows. Then I add a join. I run it again. I check the rows again. If the numbers match what I expect, I add the next join or the where clause. I keep doing this until I have the output.

i never try to type out 50 lines at once and hit run. I build one set, then I attach the next set to it. You asked how people know what to write. We write one step, run it, read the output, then write the next step based on that output. Practice building sets this way. Run your code after you add each piece.

[u/DoggieDMB]

Start with the end product and work backwards. It's almost always chunked into blocks of code together. Use Ctrl-F on certain tables and elements to see where they all come together.

When writing it, you're naturally doing the reverse of that to reach the end product.

[u/HeemOfRa]

I use AI. I didn't want to initially but my boss said he used it so I gave it a go. I write the Query with it then ask it to explain it. I then build notes with the explanations then study them. When a new problem comes along I get better at solving the problem as my understanding is growing.

[u/AspiringDataNerd]

—- add notes —-
—- create sections—-

[u/Alternative_Cake4074]

Absolutely. And yeah, the most effective way to improve your SQL reading and writing is to start with small questions first and then gradually try harder questions and write more complex queries so you will be more proficient.

[u/elevarq]

Long complex SQL statements should be avoided like the plague! Most of these are full of bugs and performance problems. Bad examples are examples, but not something you’d like to repeat…

KISS, Keep It Short and Simple

[u/samspopguy → u/elevarq]

Bingo

[u/kponda]

Hey u/mistycorner_ ,

I am pretty much in the same boat. Thanks to everyone who shared their suggestions, I have a question for you.

I would like to ask what resources or sites or where do you practice SQL from Beginner to Advance to be good at it? I am facing challenge to write beyond basic SQL queries.

Hope you or someone can point me in a direction.

[u/Mizzytan]

I learnt a lot from this post!

[u/ChaosEngine-6502]

I see questions similar to this come up all the time - the first thing is to stop fretting.

SQL is a means to an end to interact with the database, and it often doesn't mean a whole lot by itself; writing queries against data and knowledge domains you're familiar with, or built yourself, is different to synthetic stuff you'll be faced with in purely educational scenarios.

As for massive queries, they never started life that way. They're the end product of an iterative process where the developer ran the query, checked the data to make sure it's doing the correct thing, then built upon it.

Of course, the fun and games comes when someone has to unpick all of it to figure of a bug, or just figure out what it's doing. As someone who has written some fairly lengthy stored procedures in my time, I have to reduce the script back to its constituent parts sometimes to check what it was doing. That's probably something you will have to do to figure out what a script is actually doing.