* Leetcode SQL Easy Questions.docx
* Leetcode SQL Medium & Hard Questions.docx
* SQL Locked Easy Questions.docx
* SQL Locked Medium Questions.docx
* SQL Locked Hard Questions.docx
(2). The solutions are in the docx files. But you can find more discussion on leetcode.com. Here is a link to Leetcode SQL practice:
https://leetcode.com/problemset/database/
(3). References:
https://www.datageekinme.com/projects/leetcode-sql-solutions/
(This website contains not only solution but also the data to create the tables)
https://www.db-fiddle.com/
( This website is helpful for you to create tables and test your queries )