Skip to main content

Select

The SELECT keyword is used to retrieve specific columns or data from a database table. It allows you to specify what data you want to fetch, such as all columns (SELECT *) or specific ones (SELECT column1, column2). This is the first step in most SQL queries.

1. Basic Usage​

You can retrieve specific columns or all columns from a table. 

SELECT column1, column2 FROM table_name;
  • This fetches column1 and column2 from the specified table.
  • To retrieve all columns, use *: 
    SELECT * FROM table_name;

2. Column Aliases​

You can rename columns in the result set using aliases for better readability. 

SELECT column1 AS alias_name FROM table_name;

For example, SELECT first_name AS name FROM employees; will display the column first_name as name.

3. Expressions​

The SELECT statement allows you to perform calculations or apply functions on columns. 

SELECT salary * 12 AS annual_salary FROM employees;

Here, the SELECT statement calculates the annual salary based on the salary column.

4. Distinct Values​

To fetch unique values from a column, use the DISTINCT keyword. 

SELECT DISTINCT column_name FROM table_name;

This removes duplicate rows for the specified column.

5. Combining with Other Clauses​

The SELECT statement is often combined with other clauses to filter (WHERE), group (GROUP BY), sort (ORDER BY), or limit (LIMIT) the data.
Example: 

SELECT name, age 
FROM users 
WHERE age > 30 
ORDER BY age DESC 
LIMIT 5;

This fetches the top 5 users older than 30, sorted by age in descending order.

6. Subqueries​

You can use SELECT inside another query to retrieve data as part of a condition. 

SELECT name 
FROM employees 
WHERE department_id = (SELECT id FROM departments WHERE name = 'IT');

Here, the inner SELECT retrieves the department ID for "IT", and the outer query fetches employees in that department.