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SQL Interview Success: Unlocking the Top 5 Frequently Asked Queries

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 Here are the five top commonly asked SQL queries in the interviews. These you can expect in Data Analyst, or, Data Engineer interviews. Top SQL Queries for Interviews 01. Joins The commonly asked question pertains to providing two tables, determining the number of rows that will return on various join types, and the resultant. Table1 -------- id ---- 1 1 2 3 Table2 -------- id ---- 1 3 1 NULL Output ------- Inner join --------------- 5 rows will return The result will be: =============== 1  1 1   1 1   1 1    1 3    3 02. Substring and Concat Here, we need to write an SQL query to make the upper case of the first letter and the small case of the remaining letter. Table1 ------ ename ===== raJu venKat kRIshna Solution: ========== SELECT CONCAT(UPPER(SUBSTRING(name, 1, 1)), LOWER(SUBSTRING(name, 2))) AS capitalized_name FROM Table1; 03. Case statement SQL Query ========= SELECT Code1, Code2,      CASE         WHEN Code1 = 'A' AND Code2 = 'AA' THEN "A" | "A
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10 Top Differences Between Unix and Linux

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UNIX

It is an operating system which was first developed in the 1960s and has been under constant development ever since. By operating system, we mean the suite of programs which make the computer work.

It is a stable, multi-user, multi-tasking system for servers, desktops, and laptops.
UNIX systems also have a graphical user interface (GUI) similar to Microsoft Windows which provides an easy to use environment.

However, knowledge of UNIX is required for operations which aren't covered by a graphical program, or for when there is no windows interface available, for example, in a telnet session.
  • The kernel - The kernel of UNIX is the hub of the operating system: it allocates time and memory to programs and handles the filestore and communications in response to system calls. As an illustration of the way that the shell and the kernel work together, suppose a user types rm myfile (which has the effect of removing the file myfile). The shell searches the filestore for the file containing the program rm, and then requests the kernel, through system calls, to execute the program rm on myfile. When the process rm myfile has finished running, the shell then returns the UNIX prompt % to the user, indicating that it is waiting for further commands.
  • The shell - The shell acts as an interface between the user and the kernel. When a user logs in, the login program checks the username and password, and then starts another program called the shell. The shell is a command line interpreter (CLI). It interprets the commands the user types in and arranges for them to be carried out. The commands are themselves programs: when they terminate, the shell gives the user another prompt (% on our systems).
  • The adept user can customize his/her own shell, and users can use different shells on the same machine. Staff and students in the school have the tcsh shell by default.
  • The tcsh shell has certain features to help the user inputting commands.
  • Filename Completion - By typing part of the name of a command, filename or directory and pressing the [Tab] key, the tcsh shell will complete the rest of the name automatically. If the shell finds more than one name beginning with those letters you have typed, it will beep, prompting you to type a few more letters before pressing the tab key again.
  • History - The shell keeps a list of the commands you have typed in. If you need to repeat a command, use the cursor keys to scroll up and down the list or type history for a list of previous commands.

Linux


From smartphones to cars, supercomputers and home appliances, the Linux operating system is everywhere.

Android may be based on Linux, but it’s not based on the type of Linux system you may have used on your PC. You can’t run Android apps on typical Linux distributions and you can’t run the Linux programs you’re familiar with on Android.

Linux makes up the core part of Android, but Google hasn’t added all the typical software and libraries you’d find on a Linux distribution like Ubuntu. This makes all the difference.


Linux. It’s been around since the mid-‘90s, and has since reached a user-base that spans industries and continents. For those in the know, you understand that Linux is actually everywhere. It’s in your phones, in your cars, in your refrigerators, your Roku devices.

It runs most of the Internet, the supercomputers making scientific breakthroughs, and the world\'s stock exchanges. But before Linux became the platform to run desktops, servers, and embedded systems across the globe, it was (and still is) one of the most reliable, secure, and worry-free operating systems available.

For those not in the know, worry not – here is all the information you need to get up to speed on the Linux platform.

What is Linux?

Just like Windows XP, Windows 7, Windows 8, and Mac OS X, Linux is an operating system. An operating system is a software that manages all of the hardware resources associated with your desktop or laptop. To put it simply – the operating system manages the communication between your software and your hardware. Without the operating system (often referred to as the “OS”), the software wouldn’t function.

The OS is comprised of a number of pieces
  • The Bootloader: The software that manages the boot process of your computer. For most users, this will simply be a splash screen that pops up and eventually goes away to boot into the operating system.
  • The kernel: This is the one piece of the whole that is actually called “Linux”. The kernel is the core of the system and manages the CPU, memory, and peripheral devices. The kernel is the “lowest” level of the OS.
  • Daemons: These are background services (printing, sound, scheduling, etc) that either start up during boot, or after you log into the desktop.
  • The Shell: You’ve probably heard mention of the Linux command line. This is the shell – a command process that allows you to control the computer via commands typed into a text interface. This is what, at one time, scared people away from Linux the most (assuming they had to learn a seemingly archaic command line structure to make Linux work). This is no longer the case. With modern desktop Linux, there is no need to ever touch the command line.
  • Graphical Server: This is the sub-system that displays the graphics on your monitor. It is commonly referred to as the X server or just “X”.
  • Desktop Environment: This is the piece of the puzzle that the users actually interact with. There are many desktop environments to choose from (Unity, GNOME, Cinnamon, Enlightenment, KDE, XFCE, etc). Each desktop environment includes built-in applications (such as file managers, configuration tools, web browsers, games, etc).


Applications

Desktop environments do not offer the full array of apps. Just like Windows and Mac, Linux offers thousands upon thousands of high-quality software titles that can be easily found and installed. Most modern Linux distributions (more on this in a moment) include App Store-like tools that centralize and simplify application installation.

For example Ubuntu Linux has the Ubuntu Software Center which allows you to quickly search among the thousands of apps and install them from one centralized location.


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