Database Administrator Interview Question - Entry Level

Level 1: The Minion
 
 Databases at their very core are methods of storing information for later use in a safe and secure place, using a strange language that at first it seems that everybody but you can understand. As a result, at this stage you most likely have a particular project that you need to maintain or implement — one that requires vast amounts of information to be cared for and kept tidy. Learning how to navigate a database isn’t necessarily as difficult as traversing an underground lair, but you can still get lost between the tables. Bananas are optional, but tasty.

• What is a Database?

A Database Administrator needs to know what a database is before they can administer it, right? At its most basic, a database is a collection of tables, structured in such a way that it can be navigated like you would any sort of table. If you remember in math class, you may have had a number of tables that allowed you to quickly find a value if you multiplied an x and y value together — or in this case, what it would be if you were looking for a particular row and column value.

• Why should I go to all the trouble of creating a database when I have a perfectly good Excel Spreadsheet?

Scale. If you were to take a (singular) spreadsheet and a (singular) table and place them side by side, there would be effectively no difference in the data you are seeing or what you could do with it. As you go bigger and bigger with more and more tables and spreadsheets, if you have a black belt in spreadsheet-fu you can accomplish many of the same tasks that a database could do as well. The problem is, as you go larger and larger and larger, that it becomes much more difficult to be human-friendly and still be efficient when it comes to processing data. So should you replace every single spreadsheet with a database? Not necessarily, but if the data on that spreadsheet needs to be accessed quickly by multiple users simultaneously and is growing rapidly, it may be time to consider going to the dark side (they have cookies).

• What is a query?

A query in normal terms is a question, simple enough. It is the statement that is talking to the database in order to Create, Read, Update or Delete (CRUD) data. While many times a query is an actual question asking for an answer, it can also be the statement to modify, insert, or remove data in the database as well.

• What is SQL?

Structured Query Language is the basic way of asking a database server to talk to you. Whether that is in the context of asking it a question, giving it answers to questions it is asking you, or updating answers that have already been stored in the database. The art of asking the right question is critical to getting back the right data you need, which is incredibly valuable when dealing with databases, as it is very easy to receive far more data than you know what to do with, or nothing at all.

• What does ‘SELECT’ do?

SELECT in the terms of an SQL query triggers a question to the database. It looks across the specified table(s), finds the data you are looking for and then presents it to the user for consideration. Depending on the query, this can be an awful lot of data, so again, asking the right question is critical.

• What is a primary key?

A primary key is usually used as the index for a particular table — a value that the table can depend upon to be a reliable unique value in every row. When trying to pull data for a particular row, the primary key will normally be used to pull that information, usually a numeric value. For example, if you are trying to pull up data on a specific person, and that database is using their unencrypted ssn as the primary key (naughty), then that could be used in the query to identify that particular row since there could be other people present in the database with that specific name or other identifying characteristics.

• What is a Database Management System?

A Database Management System, or DBMS, is essentially the application that handles the heavy lifting between you (the user), and the raw data. The database itself is just that — the database; it cannot alter its own data any more than the average person can re-arrange their genetic code. The DBMS is what you are talking to when you are asking the questions. It is what looks at your question, thinks about it for a while, goes to the database, picks up the data, hands it back to you, and asks you to come again.

• What is the difference between a Navigational database and a Relational database?

The best way to describe a Navigational DBMS is through that of a tree. Each value was associated with another through the use of a parent, most of the time with no other direct way to access the data. Relational Databases on the other hand use values common to multiple tables to establish a unique key — making sure that they are talking on the same page so that there are many, many ways to get to the same place. To put it another way, if you were trying to get from point A to point B, a navigational database would have one specific path to get there — via a freeway. A relational database on the other hand would have options for taking the freeway, a back road, a boat, a plane, a bus and sometimes a rocket — provided that each of those methods were set up correctly to talk to each other. Most modern databases use the relational database model.

• Why do most database types not talk to each other?

In a word: money. In three words: a lotttta money. Different database vendors spend a huge amount of research time trying to find ways to give them a leg up on the competition; whether that may be by performance, storage capacity, longevity, reliability, scalability, the list goes on and on. As a result, trying to be compatible and backwards engineer every single feature of a particular database type is difficult in the extreme before you even get to the patent violations. Most databases can be simplified down to filetypes like .csv files, which can be used to transport basic data from vendor to vendor. That being said however, there would be a lot lost in translation without help from higher up.

• What is a Frontend?

For those that don’t want to see row upon row upon row of data in front of them until they go cross-eyed, a frontend is essential. In essence a management program, a frontend allows admins to be able to view and modify high level database functions without the need to use the command line for every single thing. This can be extremely useful not only for efficiency, but also for safety, as it can prevent accidental data modification. It can also allow users that are more used to a GUI application most of the utility that the CLI permits.