Jinsi ya Kufahamu Primary Keys na Foreign Keys

Kwenye database design, ni muhimu kuelewa Primary Keys na Foreign Keys.
Hizi husaidia kudhibiti uniqueness ya data na kuunganisha tables kwa usahihi.

🔹 1. Primary Key ni Nini?

Primary Key (PK) ni field ya kipekee katika table ambayo inatambulisha kila record kwa uniqueness.

Haina duplicate values.

Haiwezi kuwa null.

Mfano: Table ya students

CREATE TABLE students (
id INT(11) AUTO_INCREMENT PRIMARY KEY,
name VARCHAR(100) NOT NULL,
email VARCHAR(100) NOT NULL
);

🔍 Maelezo:

id ni primary key.

Kila student ana unique id.

AUTO_INCREMENT inasaidia kuongezwa kiotomatiki.

🔹 2. Foreign Key ni Nini?

Foreign Key (FK) ni field katika table moja inayorefer ku primary key ya table nyingine.

Inahakikisha data consistency.

Inazuia entries zisizo halali.

Mfano: Table ya students na classes

Create table ya classes

CREATE TABLE classes (
id INT(11) AUTO_INCREMENT PRIMARY KEY,
class_name VARCHAR(50) NOT NULL
);


Create table ya students

CREATE TABLE students (
id INT(11) AUTO_INCREMENT PRIMARY KEY,
name VARCHAR(100) NOT NULL,
class_id INT(11),
FOREIGN KEY (class_id) REFERENCES classes(id)
);

🔍 Maelezo:

class_id ni foreign key inayohusiana na classes.id.

Hakuna student anaweza kuwa na class_id isiyo halali.

🔹 3. Kuongeza Data Kwa Tables

Kuongeza classes kwanza

INSERT INTO classes (class_name) VALUES ('Form 1'), ('Form 2');


Kuongeza students

INSERT INTO students (name, class_id)
VALUES ('Asha', 1), ('John', 2);

🔍 Faida:

Hakuna student atakayeingizwa kwa darasa ambalo halipo.

Inahakikisha referential integrity.

🔹 4. Kutumia JOIN Kuchanganua Data

Kutoa student na darasa lake

SELECT s.name, c.class_name
FROM students s
JOIN classes c ON s.class_id = c.id;

Matokeo:
Name | Class_name
Asha | Form 1
John | Form 2

🔹 5. Vidokezo Muhimu

Kila table lazima iwe na primary key.

Foreign key inakuza uhusiano kati ya tables.

Husaidia kuunda relational database yenye data consistency.

Tumia ON DELETE CASCADE au ON UPDATE CASCADE kwa foreign keys ili kudhibiti updates/removals.

🌐 Soma Zaidi

Kwa mafunzo zaidi ya MySQL relational database design, tembelea https://www.faulink.com/
.
Utajifunza jinsi ya kuunda tables, kuunganisha data, na kudhibiti databases kwa vitendo.

📘 Hitimisho

Primary Keys na Foreign Keys ni msingi wa database design ya kitaalamu.
Zina:

Kuhakikisha uniqueness na referential integrity.

Kurahisisha JOIN operations.

Kuwezesha database yako kufanya kazi vizuri na salama.