Querying Data Commands

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Now Querying Data commands in the same exam-perfect pattern:

• One base table

• Question

• SQL

• Exact OUTPUT

• ✔ short explanation

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📘 Base Table (Used for ALL Queries)

products

product_id	product_name	category	price	age
1	Laptop	Electronics	60000	2
2	Phone	Electronics	30000	1
3	Shirt	Clothing	1500	3
4	Jeans	Clothing	2500	4
5	TV	Electronics	45000	5
6	Watch	Accessories	5000	6

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🧾 Summary Table (Querying Commands)

No.	Command	Question
1	SELECT	Retrieve specific columns
2	WHERE	Filter rows
3	ORDER BY	Sort result
4	GROUP BY	Group rows
5	HAVING	Filter groups

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1️⃣ SELECT Statement

Question: Show product name and price of all products.

SELECT product_name, price
FROM products;

✅ Output

product_name	price
Laptop	60000
Phone	30000
Shirt	1500
Jeans	2500
TV	45000
Watch	5000

✔ Retrieves selected columns
✔ Does not filter or sort data

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2️⃣ WHERE Clause

Question: Show products with price greater than 30,000.

SELECT *
FROM products
WHERE price > 30000;

✅ Output

product_id	product_name	category	price	age
1	Laptop	Electronics	60000	2
5	TV	Electronics	45000	5

✔ Filters rows based on condition
✔ Works before grouping

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3️⃣ ORDER BY Clause

Question: Show all products sorted by price (highest first).

SELECT *
FROM products
ORDER BY price DESC;

✅ Output

product_name	price
Laptop	60000
TV	45000
Phone	30000
Watch	5000
Jeans	2500
Shirt	1500

✔ Sorts result set
✔ Does not change table data

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4️⃣ GROUP BY Clause

Question: Show total number of products in each category.

SELECT category, COUNT(*) AS total_products
FROM products
GROUP BY category;

✅ Output

category	total_products
Electronics	3
Clothing	2
Accessories	1

✔ Groups rows by category
✔ Uses aggregate function

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5️⃣ HAVING Clause

Question: Show categories having more than 2 products.

SELECT category, COUNT(*) AS total_products
FROM products
GROUP BY category
HAVING COUNT(*) > 2;

✅ Output

category	total_products
Electronics	3

✔ Filters grouped results
✔ Used after GROUP BY

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🔥 WHERE vs HAVING (Quick Revision)

WHERE	HAVING
Filters rows	Filters groups
Used before GROUP BY	Used after GROUP BY
No aggregate functions	Aggregate functions allowed

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🧠 One-Line Memory Trick

Clause	Remember
SELECT	What to show
WHERE	Which rows
ORDER BY	In what order
GROUP BY	Make groups
HAVING	Filter groups

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If you want next:

• Combined queries (WHERE + GROUP BY + HAVING)

• MCQs with output prediction

• Interview traps

• Hindi explanations for exams

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