devops-exercises/tests/testcases/testcase2.md

Explain the following code:

:(){ :|:& };:

Can you give an example to some Bash best practices?

What is the ternary operator? How do you use it in bash?

A short way of using if/else. An example:

&& b="yes, equal" || b="nope"

What does the following code do and when would you use it?

diff <(ls /tmp) <(ls /var/tmp)

It is called 'process substitution'. It provides a way to pass the output of a command to another command when using a pipe | is not possible. It can be used when a command does not support STDIN or you need the output of multiple commands. https://superuser.com/a/1060002/167769

SQL

👶 Beginner

What does SQL stand for?

Structured Query Language

How is SQL Different from NoSQL

The main difference is that SQL databases are structured (data is stored in the form of tables with rows and columns - like an excel spreadsheet table) while NoSQL is unstructured, and the data storage can vary depending on how the NoSQL DB is set up, such as key-value pair, document-oriented, etc.

What does it mean when a database is ACID compliant?

ACID stands for Atomicity, Consistency, Isolation, Durability. In order to be ACID compliant, the database much meet each of the four criteria

Atomicity - When a change occurs to the database, it should either succeed or fail as a whole.

For example, if you were to update a table, the update should completely execute. If it only partially executes, the update is considered failed as a whole, and will not go through - the DB will revert back to it's original state before the update occurred. It should also be mentioned that Atomicity ensures that each transaction is completed as it's own stand alone "unit" - if any part fails, the whole statement fails.

Consistency - any change made to the database should bring it from one valid state into the next.

For example, if you make a change to the DB, it shouldn't corrupt it. Consistency is upheld by checks and constraints that are pre-defined in the DB. For example, if you tried to change a value from a string to an int when the column should be of datatype string, a consistent DB would not allow this transaction to go through, and the action would not be executed

Isolation - this ensures that a database will never be seen "mid-update" - as multiple transactions are running at the same time, it should still leave the DB in the same state as if the transactions were being run sequentially.

For example, let's say that 20 other people were making changes to the database at the same time. At the time you executed your query, 15 of the 20 changes had gone through, but 5 were still in progress. You should only see the 15 changes that had completed - you wouldn't see the database mid-update as the change goes through.

Durability - Once a change is committed, it will remain committed regardless of what happens (power failure, system crash, etc.). This means that all completed transactions must be recorded in non-volatile memory.

Note that SQL is by nature ACID compliant. Certain NoSQL DB's can be ACID compliant depending on how they operate, but as a general rule of thumb, NoSQL DB's are not considered ACID compliant

When is it best to use SQL? NoSQL?

SQL - Best used when data integrity is crucial. SQL is typically implemented with many businesses and areas within the finance field due to it's ACID compliance.

NoSQL - Great if you need to scale things quickly. NoSQL was designed with web applications in mind, so it works great if you need to quickly spread the same information around to multiple servers

Additionally, since NoSQL does not adhere to the strict table with columns and rows structure that Relational Databases require, you can store different data types together.

What is a Cartesian Product?

A Cartesian product is when all rows from the first table are joined to all rows in the second table. This can be done implicitly by not defining a key to join, or explicitly by calling a CROSS JOIN on two tables, such as below:

Select * from customers CROSS JOIN orders;

Note that a Cartesian product can also be a bad thing - when performing a join on two tables in which both do not have unique keys, this could cause the returned information to be incorrect.

SQL Specific Questions

For these questions, we will be using the Customers and Orders tables shown below:

Customers

Customer_ID	Customer_Name	Items_in_cart	Cash_spent_to_Date
100204	John Smith	0	20.00
100205	Jane Smith	3	40.00
100206	Bobby Frank	1	100.20

ORDERS

Customer_ID	Order_ID	Item	Price	Date_sold
100206	A123	Rubber Ducky	2.20	2019-09-18
100206	A123	Bubble Bath	8.00	2019-09-18
100206	Q987	80-Pack TP	90.00	2019-09-20
100205	Z001	Cat Food - Tuna Fish	10.00	2019-08-05
100205	Z001	Cat Food - Chicken	10.00	2019-08-05
100205	Z001	Cat Food - Beef	10.00	2019-08-05
100205	Z001	Cat Food - Kitty quesadilla	10.00	2019-08-05
100204	X202	Coffee	20.00	2019-04-29

How would I select all fields from this table?

Select *
From Customers;

How many items are in John's cart?

Select Items_in_cart
From Customers
Where Customer_Name = "John Smith";

What is the sum of all the cash spent across all customers?

Select SUM(Cash_spent_to_Date) as SUM_CASH
From Customers;

Tell me about your last big project/task you worked on

What was most challenging part in the project you worked on?

Why do you want to work here?

How did you hear about us?

Tell them how did you hear about them :D Relax, there is no wrong or right answer here...I think.