Assuming you want to learn Structured Query Language (SQL):
SQL is a standard language for storing, manipulating and retrieving data in databases. There are many different database management systems (DBMS) that use SQL, including MySQL, SQL Server, Oracle, PostgreSQL and SQLite.
The best site to learn SQL depends on your learning style and preferences. If you prefer a more hands-on approach, there are many interactive tutorials and exercises available online, such as:
• https://www.w3schools.com/sql/
• https://www.microsoft.com/en-us/sql-server/sql-server-2016-tutorials
• https://www.oracle.com/technetwork/ database/features/sqlt/index.html
If you prefer a more traditional learning approach, there are also many books available on SQL, such as:
• SQL For Dummies
• A Beginner’s Guide to SQL
• SQL Demystified
No matter what learning method you prefer, there are many resources available to help you learn SQL.