🔍 Data Query Language (DQL)

Last Updated: 7th January 2026

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Data Query Language (DQL) is a part of SQL used only to retrieve data from a database. It does not modify the data — it only queries (asks) the database.

• DQL is mainly based on the SELECT command
• It is used to:
  • fetch data
  • filter data
  • sort data
  • group data

Hinglish Tip 🗣: DQL ka kaam sirf data dekhna aur nikalna hota hai, data change karna nahi.

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🧾 Core DQL Command

SELECT

SELECT * FROM students;

• This query fetches all columns
• From the students table

⚠️ SELECT is the only command in pure DQL.

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🧩 Clauses Used with DQL

DQL becomes powerful when combined with SQL clauses.

Clause	Purpose (High Level)
SELECT	Choose columns
FROM	Choose table
WHERE	Filter rows
GROUP BY	Group rows
HAVING	Filter grouped data
ORDER BY	Sort result
LIMIT / OFFSET	Restrict rows
JOIN	Join multiple tables

Note: We Wil Cover Each Clause In Upcoming Tutorials

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🔢 Clause Order Matters (Very Important)

SQL clauses must follow a fixed logical order. Changing the order can cause errors or wrong results.

Order	Clause
1	SELECT
2	FROM
3	JOIN
4	WHERE
5	GROUP BY
6	HAVING
7	ORDER BY
8	LIMIT / OFFSET

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Example Showing Clause Order

SELECT department, AVG(salary)
FROM employees
WHERE salary > 30000
GROUP BY department
HAVING AVG(salary) > 40000
ORDER BY AVG(salary) DESC
LIMIT 5;

👉 Focus here is order, not logic. Each clause appears in its correct position.

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