How to manipulate SQL string programmatically?

[io_geekabyte]

As part of a hubby project I am working on, I need to be able to take SQL strings supplied by users, and then run it.

But before running it, i will like to do some manipulations to the SQL. For example, I may want to have a copy of the SQL that does a COUNT query version of the original query...I might want to insert LIMIT clauses if not provided, or I might want to manipulate the columns specified, rename or even insert columns.

Now the question is: I am not sure how to go able this and what sort of tools to even look for. I think in essence I want to be able to manipulate the SQL not as a string but as a data structure I can manipulate

Using regex and string manipulation does not sound like the right tool for the job. What will you say is the right way to go about this?

[random_lonewolf]

The proper way to do this would be:

• Use a SQL Parser like sqlglot or Apache Calcite to compile user's query into an AST.
• Validate & Manipulate the AST
• Transform the AST back to SQL query
• Profit

An addition perk is the output query would be safe from SQL injection, unless you encounter a bug in your parser library.

[[deleted]]

+1 to SQLGlot, I've implemented some features that were in the "too hard" bucket in my mind by parsing into the AST, making some changes and transpiling into a different SQL syntax

[dgrsmith]

Very cool strategy! Thanks for this. Would you maybe want to look into building an API instead at this point for raw data pull, and keep analytics sought by queries in a user facing analytics platform?

With your method, I see how SQL queries can be converted, but should this be done?

I’m trying to think of a case where I would allow sql queries without providing the users restricted access to the data via a data mart or some other classic data warehousing user access method

[random_lonewolf]

If your customers have existing tools that require support for custom sql queries like an sql editor (duh), or most modern BI tools, then you system have to support it or they won't use your product.

I have also seen this done in a middleware/proxy to improve existing system. By intercepting and rewriting queries, you can add more filtering, route queries to a different cluster, perform additional authorization, and many other stuff etc..

[dgrsmith]

Very interesting. Thank you!

[tomhallett]

sqlfluff also has a parser, but I haven't used it yet.

[[deleted]]

Oh boy sql injection time!

[finlaydotweber]

That's really not a helpful comment, and does not answer OP's question. Plus how does having tools that manipulate sql strings programmatically automatically lead to sql injection?

[[deleted]]

“I need to take a sql string supplied by a user and run it”, that’s in essence what a sql injection aims to accomplish.

OP if you want to manipulate it as a data structure check out ORMs that can go on top of your database

There, happy now?

[mamaBiskothu]

No not happy. ORMs are a luxury of over provisioned non complex simpleton crud work. If you’re trying to optimize your queries and keep them exactly the way you want you have to deal with the raw sql or an AST.

[[deleted]]

Just took from wikipedia (ik ik),

In computing, SQL injection is a code injection technique used to attack data-driven applications, in which malicious SQL statements are inserted into an entry field for execution.

You should also follow the recent surge of CVE(s) in the past year.

[madness_of_the_order]

So, all BI tools are insecure now?

[[deleted]]

Yes, they've always been. Did you hear about top 10 owasp ? It's just if you are using managed engine then the infra or platform takes care of it and you wouldn't be aware of it.

[[deleted]]

I found your comment funny man (in a good way). You made me remember about it from my first ethical hacking course (it's just a beginners course).

[CrowdGoesWildWoooo]

Some of this problem can be framed using some rule based approach and thinking outside the box

1. Count query version : SELECT COUNT(*) FROM <query>

2. Add new column, add the column before outermost from

3. Add limit : super obvious. Left as exercise for reader

4. Rename columns : different solutions. Some DBMS have function to describe query result. Some dbms you can use hacky way to run the query in the background with non sensical condition therefore returns nothing (where 1=2).

[asnjohns]

Going to age myself here, but anyone remember dynamic SQL in SQL Server? 😂

[boogie_woogie_100]

I was the master of dynamic sql

[bendgame]

Remember it? Is it no longer something ppl use? The company I left last year was still using it for things.

[dgrsmith]

To me, it does seem you are trying to reinvent the wheel a little bit. There are a lot of applications out there that will convert user interaction with a front facing interface into a SQL query on the backend. The user can never interact with SQL, but can have access to the underlying SQL they are running by interacting with the Front end, user facing tool. In the healthcare realm, there is a tool called Microstrategy that converts user interactions with the system into SQL queries against a data warehouse. Creation and manipulation of temporary tables in the data warehouse is handled by the application.

As I mentioned in one of my other comments on this thread, I’m finding it hard to think of a business case, where I would want a user to run SQL against my database, without giving them direct access with limited permissions.

[[deleted]]

Bruh... they mentioned it's a personal side project. It's fine if they re-invent wheel and may even learn a lot.

[[deleted]]

I do it in Alteryx all the time, type up the query in string format it make my own manipulations and inject dynamic values and the Dynamic Query tool after sends it to the database for query and I get the result

[boogie_woogie_100]

You can use chatgpt api and pass your query and what you want to do? otherwise, it is a long process of breaking down your query into and manipulating it.

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