Questions every good Database/SQL developer should be able to answer [closed]

Answer 1

The different types of JOINs:

• INNER JOIN
• LEFT and RIGHT OUTER JOIN
• FULL JOIN
• CROSS JOIN

See Jeff Atwood's Visual Explanation of JOINs

• What is a key? A candidate key? A primary key? An alternate key? A foreign key?

• What is an index and how does it help your database?

• What are the data types available and when to use which ones?

Answer 2

• Explain possible constraints on tables
• Explain views (and materialized)
• Explain sequences
• Explain triggers

Answer 3

What explain plan does and how interpret the results you get from it.

Answer 4

Almost everything is mentioned here. I would like to share one question which I was asked by a senior manager on database. I found the question pretty interesting and if you think about it deeply, it sort of has lot of meaning in it.

Question was - How would you describe database to your 5 year old kid ?

Answer 5

• What are the downsides of using adhoc/on-the-fly SQL statements and what would you do instead?

This area can have a huge impact on performance and security of the db. Get this wrong, and you could end up in a world of pain.

• In what situations would you use adhoc/on-the-fly SQL statements?

Because there is always an exception to the rule :)

Answer 6

Why should we hire you when we have a sophisticated application using a properly-optimized ORM and implementing caching systems such as memcached?

This is a serious question, they should be able to justify their existence. As Jeff Atwood likes to say "Hardware is Cheap, Programmers are Expensive"