The Relational Model
Relational, model, mein, DATA, ko, TABLES, mein, ORGANIZE, kiya, jaata hai — HAR, TABLE, EK, SPECIFIC, ENTITY, (jaise, users, orders) ko, REPRESENT, karti, hai. HAR, ROW, EK, INDIVIDUAL, RECORD, hai, HAR, COLUMN, EK, SPECIFIC, PIECE, OF, INFORMATION, hai.
Tables, ke, BEECH, RELATIONSHIPS, FOREIGN, KEYS, se, DEFINE, HOTE, HAIN — jaise, EK, order, TABLE, mein, user_id, COLUMN, users, TABLE, ke, id, ko, REFERENCE, karta hai.
-- Do related tables:
CREATE TABLE users (id INT PRIMARY KEY, name VARCHAR(100));
CREATE TABLE orders (
id INT PRIMARY KEY,
user_id INT,
amount DECIMAL(10,2),
FOREIGN KEY (user_id) REFERENCES users(id)
);- Tables = entities, Rows = records, Columns = attributes
- Foreign keys, se, tables, ke, beech, relationships, DEFINE, hote, hain
- Data duplication, avoid, karके, consistency, maintain, ki, jaati hai
ER, diagrams, VISUALLY, represent, karte, hain, ki, TABLES, (entities) EK, dusre, se, KAISE, RELATED, HAIN — database, design, karne, se, PEHLE, ER, diagram, banaна, EK, COMMON, practice, hai, complex, schemas, ke, liye.
Many-to-many, relationships, ko, DIRECTLY, represent, NAHI, kiya, ja, sakta — EK, "junction" (ya, "pivot") table, chahiye, HOTI, hai, DO, foreign, keys, ke, saath, — jaise, students, aur, courses, ke, beech, enrollments, table.
CREATE TABLE enrollments (
student_id INT,
course_id INT,
PRIMARY KEY (student_id, course_id),
FOREIGN KEY (student_id) REFERENCES students(id),
FOREIGN KEY (course_id) REFERENCES courses(id)
);