What is the difference between SQL, Oracle, MySQL, and SQL Server?

If a table contains duplicate rows, will a query display duplicate values by default? How can you eliminate duplicate rows from a query result?

What are the different DDL commands in SQL? Give a description of their purpose.

What is a unique constraint? How is it different from a primary key?

What is a synonym?

What is a primary key?

What is the difference between SQL and PL/SQL?

What is the difference between SQL and T-SQL?

What is a surrogate key?

What is a view? When would you use one?