Database keys

Database keys are essential for organizing and managing data effectively. In this post, we'll explore ten key concepts that every IT professional should know.

1. 🗝 𝗣𝗿𝗶𝗺𝗮𝗿𝘆 𝗞𝗲𝘆
- A unique identifier for each record in a table.
- Cannot be null.
- Ensures that each row is unique.

2. 🌉 𝗙𝗼𝗿𝗲𝗶𝗴𝗻 𝗞𝗲𝘆
- A field in one table that refers to the Primary Key of another table.
- Establishes relationships between tables.

3. 🧩 𝗖𝗼𝗺𝗽𝗼𝘀𝗶𝘁𝗲 𝗞𝗲𝘆
- A combination of two or more columns that uniquely identifies each record.
- Useful when a single column can't uniquely identify a record.

4. 💪 𝗦𝘂𝗽𝗲𝗿 𝗞𝗲𝘆
- One or more columns that can uniquely identify a record.
- A Primary Key is a type of Super Key.

5. 🏅 𝗖𝗮𝗻𝗱𝗶𝗱𝗮𝘁𝗲 𝗞𝗲𝘆
- A column or set of columns that could be the Primary Key.
- Must be unique.

6. 🔍 𝗨𝗻𝗶𝗾𝘂𝗲 𝗞𝗲𝘆
- Ensures uniqueness for a column or column combination.
- Similar to Primary Key but allows one null value.

7. 🛤 𝗔𝗹𝘁𝗲𝗿𝗻𝗮𝘁𝗲 𝗞𝗲𝘆
- A Candidate Key that isn't the Primary Key.
- Another option for a unique identifier.

8. 🍃 𝗡𝗮𝘁𝘂𝗿𝗮𝗹 𝗞𝗲𝘆
- A key that's a natural part of the data, like an email address.

9. 🎭 𝗦𝘂𝗿𝗿𝗼𝗴𝗮𝘁𝗲 𝗞𝗲𝘆
- An artificial key created when no natural unique identifier exists.

10. 🔑 𝗦𝗲𝗰𝗼𝗻𝗱𝗮𝗿𝘆 𝗞𝗲𝘆
- Used for data retrieval, not identification.
- Helps create non-clustered indexes.

Syntax Error!!!

Cause you can't declare the same variable two times. The variable num is declared twice within the same scope: once using var and then using let. Redeclaring a variable with let or const in the same scope is not allowed, leading to a syntax error.

+ operator will first convert the string to a numeric value.
so "0" -> 0
after that, it's post incrementing, so it will not increment
thus output will remain 0

P.S : There are two types of increment (post & pre)

Post (a++) will print first then increment
Pre (++a) will increment first then print

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100+ Practice Questions

❍ C/C++
❍ Python
❍ JavaScript
❍ Java
❍ C#
❍ Golang

➊ Simple Numbers

➀ Find a digit at a specific place in a number
➁ Find count of digits in a number
➂ Find the largest digit
➃ Find the 2nd largest digit
➄ Find the kth largest digit
➅ Find the smallest digit
➆ Find the 2nd smallest digit
➇ Find the kth smallest digit
➈ Find generic root (sum of all digits) of a number
➉ Reverse the digits in a number
➀➀ Rotate the digits in a number
➀➁ Is the number a palindrome?
➀➂ Find sum of 'n' numbers
➀➃ Check if a number is perfect square
➀➄ Find a number in an AP sequence
➀➅ Find a number in a GP sequence
➀➆ Find a number in fibonacci sequence
➀➇ Check number divisibility by 2, 3, 5, 9
➀➈ Check if a number is primary or not
20. Given a number, print all primes smaller than it
➁➀ Check if a number is circular prime or not
➁➁ Find all prime factors of a number
➁➂ Find the GCD of 2 numbers
➁➃ Find the LCM of 2 numbers
➁➄ Find the factorial of a number
➁➅ Find the exponentiation of a number

➋ Unit Conversion

➀ Number Base (Binary, Octal, Hexadecimal, Decimal)
➁ Weight (gram, kg, pound)
➂ Height (cm, m, inch, feet)
➃ Temperature (centigrade, fahrenhite)
➄ Distance (km, mile)
➅ Area (m², km², acre)
➆ Volume (ltr, gallon)
➇ Time (sec, min, hour)
➈ Currency

➌ Calculator

➀ Loan EMI Calculator
➁ Fixed Deposit Returns Calculator
➂ Interest Calculator
➃ BMI Calculator
➄ Item Price (considering tax, discount, shipping)
➅ Tip Calculator

➍ Geometry

➀ Find distance between 2 points
➁ Given 2 sides of a right angle triangle, find the 3rd
➂ Find 3rd angle of a triangle when 2 are given
➃ Area of a triangle when 3 sides are given
➄ Area of a right angle triangle
➅ Perimeter of a Square
➆ Area of a Square
➇ Perimeter of a Rectangle
➈ Area of a Rectangle
➉ Circumference of a Circle
➀➀ Area of a Circle
➀➁ Circumference of a Semi-Circle
➀➂ Area of a Semi-Circle
➀➃ Area of a Ring
➀➄ Circumference of an Ellipse
➀➅ Area of an Ellipse
➀➆ Suface Area of a Sphere
➀➇ Volume of a Sphere
➀➈ Surface Area of a Hemisphere
20. Volume of a Hemisphere
➁➀ Surface area of a Cube
➁➁ Volume of a Cube
➁➂ Surface area of a Cylinder
➁➃ Volume of a Cylinder

➎ Vector

➀ Find Scalar Multiplication of a vector
➁ Find addition/subtraction of vectors
➂ Find magnitude of a vector
➃ Find an unit vector along a given vector
➄ Find dot product of 2 vectors
➅ Find cross product of 2 vectors
➆ Check if 2 vectors are orthogonal

➏ Matrix

➀ Find the determinant of a matrix
➁ Find Scalar Multiplication of a matrix
➂ Find addition/subtraction of matrices
➃ Find the transpose of a matrix
➄ Find if 2 matrices are orthogonal
➅ Find inverse of a 2x2 and 3x3 matrix

➐ Set

➀ Find Union of 2 sets
➁ Find Intersection of 2 sets
➂ Find the Difference of 2 sets
➃ Find the Symmetric Difference of 2 sets
➄ Find if a set is subset/superset of another set
➅ Find if 2 sets are disjoints

➑ Special Numbers

➀ Strong Number
➁ Perfect Number
➂ Armstrong Number
➃ Harshad Number
➄ Kaprekar Number
➅ Lychrel Number
➆ Narcissistic Decimal Number
➇ Lucus Number
➈ Catalan Number
➉ Duck Number
➀➀ Ugly Number
➀➁ Abundant Number
➀➂ Deficient Number
➀➃ Automorphic Number
➀➄ Magic Number
➀➅ Friendly Pair Numbers
➀➆ Neon Number
➀➇ Spy Number
➀➈ Happy Number
20. Sunny Number
➁➀ Disarium Number
➁➁ Pronic Number
➁➂ Trimorphic Number
➁➃ Evil Number
➁➄ Amicable Pairs

🚥 Last Words

⬘ If you want to excel in programming, practice a lot.

⬙ Problems based on numbers are easy to start with and they help in improving your analytical skills.