Complex Queries in SQL 

 Complex Query kya hoti hai?

Complex Query woh hoti hai jo basic SELECT se zyada advance ho. Isme hum:

• -> Multiple tables ka use karte hain (JOINs)

• -> Queries ke andar queries (Subqueries)

• -> Grouping aur filtering (GROUP BY, HAVING)

• -> Data merge karte hain (UNION)

• -> Ya phir conditions lagate hain (CASE)

 Complex queries se hum real-life jaise problems solve kar sakte hain jahan simple query kaam nahi karti.

 Complex Queries ke Main Parts

Chaliye dekhte hain kya-kya cheezein ek complex query banati hain:

1. JOIN

Do ya zyada tables ka data jodne ke liye.

2. Subquery (Nested Query)

Ek query ke andar doosri query.

3. Aggregate Functions

Jaise SUM(), AVG(), COUNT() ke saath GROUP BY.

4. Set Operators

Jaise UNION, INTERSECT, EXCEPT.

 Example Tables

Students Table

Departments Table

 Example 1: JOIN ka Use

Q: Har student ka naam aur uska department naam chahiye.

Output:

 Yahan JOIN se dono tables ka data joda gaya hai.

 Example 2: Subquery ka Use

Q: Aise students jinki age average se zyada ho.

Agar average age 21 hai to output:

 Yahan andar wali query AVG(Age) nikaal rahi hai.

 Example 3: GROUP BY + HAVING

Q: Har department mein kitne students hain, sirf wahi dikhayein jahan count 1 se zyada ho.

 GROUP BY group banata hai aur HAVING us par condition lagata hai.

 Example 4: UNION ka Use

Q: Students aur departments ke naam ek hi column mein chahiye.

 UNION se dono results combine ho jaate hain (duplicate hata ke).

 Example 5: CASE Statement

Q: Har student ke age group ko category mein dikhana hai.

 CASE conditional logic ke liye use hota hai.

 Complex Queries ke Components Summary

 Tips for Students

• -> Pehle simple query likho

• -> Complex query ko steps mein socho

• -> AS (alias) ka use karo clarity ke liye

• -> Practice karo real examples par