SELECT COMMAND

 The DQL (Data Query Language) is a subset of SQL used to retrieve data from the database. In essence, DQL focuses on querying data stored in tables, and its most common command is SELECT.

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1. DQL Commands

The primary command in DQL is:

• SELECT: Used to retrieve data from one or more tables.

DQL allows you to:

• Specify which columns or rows to retrieve.
• Filter data using conditions.
• Sort data.
• Aggregate and group data.
• Join data from multiple tables.

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2. Syntax

Basic Syntax

sql

SELECT column1, column2, ...
FROM table_name
WHERE condition;

• column1, column2: Columns to retrieve.
• table_name: The table to query data from.
• condition: Filter to retrieve specific rows.

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3. Types of Queries

A. Retrieve All Columns

Retrieve all columns from a table:

sql

SELECT * 
FROM employees;

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B. Retrieve Specific Columns

Retrieve only specific columns:

sql

SELECT emp_id, emp_name, salary
FROM employees;

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C. Apply Filtering with WHERE

Retrieve rows based on conditions:

sql

SELECT emp_id, emp_name, salary
FROM employees
WHERE department_id = 20;