GROUP BY Example: Student Subject Marks Raju Math 80 Pooja Math 90 Amit Science 70 Neha Science 60 Output: So GROUP BY = Group then summarize. ORDER BY Example: Output: So ORDER BY = Sorting (like arrange in queue). Quick Analogy (Cricket Example): Imagine a cricket match scoreboard. Super-Simple Recap for Freshers:
Aggregate = “Total / Summary”. In SQL, aggregate functions are used to calculate values from multiple rows together (instead of checking each row one by one). Example: In a class of students, instead of checking every student’s marks separately, we calculate total marks, average marks, highest marks, etc. Common Aggregate Functions: Real-Life Analogy (Cricket Example): … Read more
Imagine you have a big dictionary .If you want to find the meaning of the word “Cricket”, In SQL, Index = shortcut for the database to find data faster. What are Indexes? Types of Indexes in SQL: Quick Recap for Freshers:
Constraints are like rules we put on a table’s columns to control what kind of data can go inside. Think of it like traffic rules: Types of Constraints (with Simple Examples) NOT NULL Means the column cannot be empty.Like in college admission form → Name is mandatory. Example: You must enter a name, otherwise error. … Read more
What is Denormalization? Example: Imagine you have a normalized database with these two tables: 1. Students Table StudentID Name ClassID 1 Rahul 101 2 Priya 102 2. Classes Table ClassID ClassName 101 Maths 102 Science his is normalized (no repeated data). But if you want to show a list of students with their class name, … Read more
Normalization is the process of organizing data in a database so that: Think of it like arranging your room: Why Do We Normalize? Types of Normalization (Normal Forms) Normalization is done in steps called Normal Forms (NF). First Normal Form (1NF) Example: Bad table: student_id name subjects 1 Ramesh Maths, Science 2 Priya Arts, Maths … Read more
DELETE removes rows (data) from a table, but the table structure remains. Example: TRUNCATE removes all rows from a table in one go. Example: Removes all students, but the students table is still there (empty). DROP deletes the entire table (structure + data). Example: Removes the table itself. Now students doesn’t exist anymore. Quick Comparison … Read more
INNER JOIN returns only the rows where matching values exist in both tables. LEFT JOIN returns all rows from the left table, and the matching rows from the right table. Example Let’s say we have two tables: students student_id name 1 Ramesh 2 Priya 3 Amit marks mark_id student_id subject marks 1 1 Maths 90 … Read more