Lossless Join Decomposition in DBMS 

 Decomposition kya hota hai?

DBMS mein kabhi-kabhi ek badi table ko chhoti-chhoti tables mein todna padta hai, jise kehte hain Decomposition.

Isse fayda yeh hota hai ki:

• Data repeat nahi hota (Redundancy kam hoti hai),

• Data clean aur consistent rehta hai.

Lekin jab table ko todte hain, to humein ensure karna hota hai ki data ka loss na ho.

 Lossless Join Decomposition kya hota hai?

Lossless Join Decomposition ka matlab hai:

Jab aap ek badi table ko chhoti tables mein divide karte ho aur baad mein join karke original table wapas bana lete ho — bina data loss ke. 

 Lossless ka simple matlab:

• Lossless = No data loss after joining back

• Lossy = Data lost ho gaya ya galat data aa gaya

 Lossless Join kyun important hai?

• Data accurate rehta hai

• Redundancy kam hoti hai

• Normalization ke time data safe rehta hai

 Example se samjho:

 Original Table: Student

 Ab isko do parts mein todte hain:

Student1(RollNo, Name)
Student2(RollNo, Course, Dept)

Student1:

Student2:

 Join karte hain dono tables ko (on RollNo):

 Yehi original table tha → Lossless Join Decomposition hai.

 Lossless hone ka Rule (Functional Dependency se):

Agar relation R ko R1 aur R2 mein todte ho to lossless hone ke liye:

R1 ∩ R2 → R1 ya R1 ∩ R2 → R2

 Yani, jo columns dono tables mein common hain, unse hum poori table ka data nikal sakein.

 Summary Table