SQL Queries and Subqueries | Database Management System In Hindi & Urdu

Published: 26 March 2023
on channel: Hafi Academy
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SQL (Structured Query Language) is a programming language used to manage and manipulate relational databases. SQL queries are used to retrieve data from databases by specifying the criteria for selecting specific data.

A SQL query is a statement use to retrieve data from one or more tables in a database. It typically consists of a SELECT statement, which specifies the columns to be retrieved, a FROM clause, which specifies the table or tables from which to retrieve the data, and one or more optional clauses such as WHERE, GROUP BY, HAVING, and ORDER BY to filter, group, and sort the data.

Subqueries are queries that are nested within another query, allowing for more complex queries to be performed. A subquery is enclosed in parentheses and can be used in the SELECT, FROM, WHERE, or HAVING clause of the outer query.

Subqueries can be used to:

Filter data based on the results of another query.
Retrieve data from a related table based on a condition.
Calculate an aggregate value based on a subset of data.
For example, a subquery can be used to find the average salary of employees in a department, and then retrieve the names of all employees whose salary is greater than the average.

Here's an example of a SQL query with a subquery:

SELECT name, department, salary
FROM employees
WHERE salary (SELECT AVG(salary) FROM employees WHERE department = 'Marketing');

This query retrieves the name, department, and salary of all employees in the Marketing department whose salary is greater than the average salary of all Marketing employees. The subquery calculates the average salary of Marketing employees .In Hindi and Urdu
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