How can improve SQL that someone's query?

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I am new to on SQL and I want to know that is there any tricky method for understanding someone's query in SQl? for example we developers generaly work on project, that written by a few years ago etc.etc. and when we face to database layer though sql we can not understanding what this query do?

What I have tried:

I improve my sql skills but still I have problem.

Posted 11-Oct-22 9:47am

vor_zakon_developer

Updated 11-Oct-22 22:55pm

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Member 8428760 11-Oct-22 16:36pm

If there are no comments explaining it, then what I usually do is scan the query and find the tables that it uses. Then you can see what columns out of the tables they are pulling. The rest of the query will be filtering what data they pull and manipulating the data they get. The query types are select, insert, update, delete. Focus on the select type statements and the rest will be easy.

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CHill60 · Answer 1 · 2022-10-11T22:55:00

You can't really understand a SQL query in complete isolation.

Try to understand what the author thinks they are returning from the database - where is the SQL used, what labels are used to describe the data in the Presentation layer, what is the title of the site/page/application - all these things can give you clues.

Next - see the comment from @User-8393253 - look at the tables and databases used. Is there any database documentation available, are the tables names / column names meaningful to help you work out what is happening - gain more clues.

Next - select sample data from the query (e.g. TOP 1000) - look at the data itself, what story is it telling you.

When you have finished all of that, have a better understanding of the database and the data then introduce peer review or other governance that insists on at least a minimum of documentation - e.g. comments that explain what the query is meant to do, for future use :laugh: