SQL Questions

Sometimes employers are hiring for a specific position where a specific language is used. In these cases, the employer might prefer to hire someone who is already well-versed with that language. Here are some questions specific to SQL (though most of them are relevant to any object-oriented language.)

Some forms on web pages except values that are used in searches. How can you prevent SQL injection?
How do you write a group by statement?
What is a foreign key?
What is a cursor?
If you have a table with duplicate values, how would you write a query that returns only the duplicate values?
What is a View?