he SELECT statement is one of the most fundamental commands in SQL. It is used to retrieve data from a database. By using SELECT, you can specify exactly which data you want to view and how it should be presented.
Basic Syntax
The basic syntax of a SELECT statement is:
SELECT column1, column2, ...
FROM table_name;
- SELECT – specifies the columns you want to retrieve.
- FROM – specifies the table from which to retrieve the data.
Example:
SELECT first_name, last_name
FROM employees;
This query retrieves the first_name and last_name columns from the employees table.
Selecting All Columns
To retrieve all columns from a table, use the asterisk (*):
SELECT *
FROM employees;
This will return every column in the employees table.
Using WHERE Clause
The WHERE clause allows you to filter records based on specific conditions.
Example:
SELECT first_name, last_name
FROM employees
WHERE department = 'Sales';
This query retrieves only the employees who work in the Sales department.
Using DISTINCT
The DISTINCT keyword ensures that the query returns unique values only.
Example:
SELECT DISTINCT department
FROM employees;
This query lists all the unique departments in the employees table.
Using ORDER BY
The ORDER BY clause sorts the result set by one or more columns.
Example:
SELECT first_name, last_name
FROM employees
ORDER BY last_name ASC;
This query retrieves employees’ names sorted alphabetically by last_name.
Using LIMIT
The LIMIT clause restricts the number of rows returned.
Example:
SELECT first_name, last_name
FROM employees
LIMIT 5;
This query retrieves only the first five rows from the employees table.
Summary
- SELECT is used to fetch data from a database.
- Columns can be specified individually or with
*for all columns. - Filters can be applied using WHERE.
- Unique values can be retrieved using DISTINCT.
- Results can be sorted using ORDER BY.
- Limit the number of results using LIMIT.