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
A Foreign Key is a column in one table that is used to connect it with another table. Think of it like a relationship: So: Rules of Foreign Key Example in MySQL Table 1: students Data: student_id name 1 Ramesh 2 Priya Table 2: marks Here: Insert Data sqlINSERT INTO marks VALUES (1, 1, ‘Maths’, … Read more
A Primary Key is a column (or set of columns) in a table that uniquely identifies each row. Think of it like your Aadhar Number or Roll Number in college: That’s exactly how a primary key works in SQL. Rules of Primary Key Example in MySQLTable without primary key: Here, nothing stops two students from … Read more
A subquery is a query (SQL statement) inside another query.It’s like asking one question inside another question to get your final answer. Syntax: Example of a Subquery Imagine two tables: students id name class_id 1 Ramesh 101 2 Priya 102 3 Amit 101 classes class_id class_name 101 Science 102 Arts Question: Find students who belong … Read more
Here’s a simple and clear explanation of the difference between WHERE and HAVING in SQL: Quick Explanation Difference Between WHERE and HAVING Feature WHERE HAVING Purpose Filters rows before grouping (used on individual rows) Filters groups after grouping (used with GROUP BY) Used With Any table or query Only with GROUP BY or aggregate functions … Read more
What is SQL? SQL (Structured Query Language) is a standard programming language used to communicate with and manage data in relational database management systems (RDBMS) like MySQL, PostgreSQL, Microsoft SQL Server, and Oracle. What are the different types of SQL statements? DDL, DML, DCL, TCLWhat is the difference between WHERE and HAVING?What is a primary key?What is a foreign key?What is the … Read more