This might suit your needs. I wrote an app in Python that can generate a CRM and sales database with sample data. The readme is ok but PM me if you need help: https://github.com/cavebutter/datagen More on reddit.com

Most DBMSes come with sample databases. You can write lots of interesting queries against them, and usually a tutorial accompanies the database in the documentation. For MySQL, there's the Employees sample database: https://dev.mysql.com/doc/employee/en/ and also the Sakila sample database: https://dev.mysql.com/doc/sakila/en/ Also: Kaggle is full of sample data: https://www.kaggle.com/ Wikipedia publishes all of the content of Wikipeida as SQL scripts for MySQL, plus as XML files. You can get that data (or subsets of it) and play around. Load a small one or a huge one, get to work writing queries on it. Here's a github repository with lots of interesting data sets: https://github.com/awesomedata/awesome-public-datasets FiveThirtyEight has lots of neat sets: https://data.fivethirtyeight.com/ There's a website called "Relational Data Set Repository" which has bunches of sets: https://relational.fit.cvut.cz/ data.world has more than 30 data sets: https://data.world/datasets/database Someone manages this git repository that lists some interesting sets: https://github.com/joschout/RelationalDatasets More on reddit.com

This should be good for basics https://www.geeksengine.com/database/problem-solving/northwind-queries-part-1.php WHen youre ready to up your game you could get the stackoverflow database and then start doing more complicated exercises. i feel like it helps to have specific things listed out for you that you'd need to know about. So Here is a short list of things off the top of my head Islands and Gaps. Youll eventually need to know what this issue is and how to solve. Google it as its a pretty fun read in almost every article ive seen about it. Relational Division. Again another technique used to solve for specific criteria Pivoting data. Most o fthe time you'll wanna store data as rows, but sometimes the requirement is to display as columns. Knowing how to pivot data is important. Recursive CTE's. pretty simple stuff but knowing when its appropriate to use them is important. Different techniques to find duplicate data. Sub string extraction. Youre eventually going to run into shitty data and knowing how to find sub strings is going to be needed. Dynamic SQL and how to use it properly. I mainly mean how to use system table to help you build code that writes code for you. A lot of simple ETL procs can be written this way. it saves you time. Understanding window functions like ROW_NUMBER(), RANK() and DENSE_RANK(). I use these quite a bit for various different reasons. the PARTITION BY clause is something you should wrap your head aorudn. This is what I can think of right now. There's tons more, but these will keep you busy for a minute. More on reddit.com

I'm going to go in a different direction than others suggesting leetcode here. Have you considered working on a small side project and using a local SQL-based database? You can import an existing dataset into one, and you will learn a lot from it. More on reddit.com