Domain Relational Calculus (DRC) kya hota hai?

Domain Relational Calculus ek non-procedural query language hai jo databases mein use hoti hai.
Iska matlab hai: hum batate hain kya chahiye, lekin ye nahi batate ki kaise milega.

Ye domain variables ke saath kaam karta hai — jo ki table ke columns se values ko represent karte hain.

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 TRC vs DRC (Basic Difference)

 DRC ka Basic Syntax

• <x1, x2, ..., xn> = domain variables (columns ke values).

• P(...) = condition ya predicate (logical expression).

 Example Table: Student

 DRC ke Example Queries

 1. Sab students ke naam chahiye

Isme:

• <N> ka matlab hai humein naam chahiye.

• ∃R aur ∃A ka matlab hai koi bhi roll number aur age ho sakti hai.

• Yani: “Woh sab names do jinke liye koi roll number aur age exist karti hai.”

 Output:

 2. Un students ke naam jinki age 18 se zyada hai

 Output:

 3. Roll number of student jiska naam “Bob” hai

 Output:

 Domain Relational Calculus ke Features

•  Non-Procedural: Bas batana hota hai kya chahiye, kaise laana hai wo DBMS handle karta hai.

•  Safe Expressions: Sirf wahi data return hota hai jo database mein exist karta hai.

•  Logic pe based: Logical operators jaise:

  • ∃ (There exists)

  • ∀ (For all)

  • AND, OR, NOT use hote hain.

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 SQL vs DRC (Comparison)

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 Final Notes 

• -> DRC mainly theory ke liye use hota hai — jaise ki university exams ya concept understanding.

• -> SQL daily life mein zyada use hota hai, lekin DRC aapke logical thinking ko strong banata hai.

• -> Agar aapko relational logic samajhna hai, toh DRC ek important concept hai.