The SQL SELECT statement is the cornerstone of data retrieval in relational databases. It is used to query the database and fetch data based on specified criteria.

The basic syntax of the SELECT statement is as follows:

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

• SELECT: Specifies the columns to be retrieved.
• FROM: Specifies the table from which the data should be fetched.
• WHERE: Specifies the conditions that must be met for a row to be included in the result set.

Fetching All Columns: To retrieve all columns from a table, you can use the wildcard character (*):

SELECT *
FROM table;

Filtering Data: The real power of the SELECT statement lies in its ability to filter data based on specific conditions. The WHERE clause allows you to define conditions that must be satisfied for a row to be included in the result set. For example:

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

Sorting Results: Sorting data is another essential aspect of data retrieval. The ORDER BY clause allows you to sort the result set based on one or more columns, either in ascending (ASC) or descending (DESC) order:

SELECT *
FROM customers
ORDER BY last_name ASC;

Limiting Results: In situations where you only need a specific number of rows from the result set, you can use the LIMIT clause. This is particularly useful for optimizing performance when dealing with large datasets:

SELECT *
FROM orders
LIMIT 10;

Aggregate Functions: The SELECT statement can also be enhanced with aggregate functions like COUNT, SUM, AVG, MIN, and MAX. These functions enable you to perform calculations on groups of rows, providing valuable insights into the dataset:

SELECT department, AVG(salary) as avg_salary
FROM employees
GROUP BY department;