SQL SELECT Keyword

 The SQL SELECT keyword is used to retrieve data from a database. It is one of the most fundamental and widely used commands in SQL (Structured Query Language). The SELECT statement allows you to query and extract specific information from a table or multiple tables, based on certain conditions.

Basic Syntax:

SELECT column1, column2, ...
FROM table_name;

• column1, column2, ...: The columns you want to retrieve from the table. You can list specific columns, or use * to select all columns.
• table_name: The name of the table from which you want to retrieve data.

Examples:

1. Select all columns from a table:

   SELECT * FROM employees;
   

   This retrieves all columns and rows from the employees table.

2. Select specific columns from a table:

   SELECT first_name, last_name FROM employees;
   

   This retrieves the first_name and last_name columns from the employees table.

3. Select distinct (unique) values:

   SELECT DISTINCT department FROM employees;
   

   This retrieves a list of unique departments from the employees table, removing duplicates.

4. Select with a condition (using WHERE clause):

   SELECT first_name, last_name FROM employees WHERE department = 'HR';
   

   This retrieves the first_name and last_name of employees who work in the 'HR' department.

5. Order the results (using ORDER BY clause):

   SELECT first_name, last_name FROM employees ORDER BY last_name;
   

   This retrieves employee names and orders the results alphabetically by last_name.

6. Limit the number of results (using LIMIT or FETCH clause):

   SELECT first_name, last_name FROM employees LIMIT 5;
   

   This retrieves only the first 5 rows from the employees table.

Combining with Other Clauses:

You can also combine the SELECT statement with other SQL clauses like:

• WHERE: Filters rows based on a condition.
• ORDER BY: Sorts the results.
• GROUP BY: Groups rows based on column values, often used with aggregate functions.
• JOIN: Combines rows from two or more tables based on a related column.

Example with multiple clauses:

SELECT first_name, last_name, department
FROM employees
WHERE department = 'IT'
ORDER BY last_name ASC;

This retrieves the first_name, last_name, and department of employees in the 'IT' department, ordered by last_name in ascending order.

In short, the SELECT keyword is essential for querying and extracting data from a database in SQL.