Select Query in SQL

Select Query in SQL

Introduction: The SELECT statement is one of the most fundamental and frequently used queries in SQL. It is used to retrieve data from one or more tables in a database. This document provides a comprehensive overview of the SELECT query syntax and examples.

Syntax: The basic syntax of the SELECT query is as follows:

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

Explanation:

• SELECT: The SELECT keyword is used to indicate that we want to retrieve data from the database.
• column1, column2, ...: Specify the column names you want to retrieve from the table. You can select specific columns or use "*" to select all columns.
• FROM: Specifies the table or tables from which you want to retrieve the data.
• table_name: The name of the table from which you want to retrieve data.
• WHERE: This optional clause is used to specify conditions that the retrieved data must satisfy. It filters the data based on specific criteria.

Examples:

1. Select all columns from a table:

sql
SELECT * FROM employees;

2. Select specific columns from a table:

sql
SELECT first_name, last_name, salary FROM employees;

3. Select columns with alias names:

sql
SELECT first_name AS "First Name", last_name AS "Last Name" FROM employees;

4. Select data with a condition:

sql
SELECT * FROM employees WHERE department = 'IT';

5. Select data with multiple conditions:

sql
SELECT * FROM employees WHERE department = 'IT' AND salary > 50000;

6. Select data with sorting:

sql
SELECT * FROM employees ORDER BY last_name ASC;

7. Select data with limited rows:

sql
SELECT * FROM employees LIMIT 10;

8. Select data with calculated columns:

sql
SELECT first_name, last_name, salary, salary * 0.1 AS "Bonus" FROM employees;

Conclusion: The SELECT query is a powerful tool in SQL that allows you to retrieve specific data from one or more tables in a database. By understanding its syntax and using various clauses, conditions, and functions, you can effectively retrieve and manipulate data to meet your requirements.