SELECT

-- Retrieves the specified columns.
SELECT column1, column2 FROM table_name;

-- Retrieves all columns.
SELECT * FROM table_name;

-- Retrieves a column with an alias.
SELECT column_name AS alias FROM table_name;

-- Retrieves unique values, excluding duplicate rows.
SELECT DISTINCT column_name FROM table_name;

-- Retrieves the name and department from the employees table.
SELECT name, department FROM employees;

-- Retrieves all columns from the employees table.
SELECT * FROM employees;

-- Retrieves columns with aliases.
SELECT name AS full_name, salary AS monthly_salary FROM employees;

-- Retrieves a list of departments with duplicates removed.
SELECT DISTINCT department FROM employees;

-- You can also assign an alias to a calculated expression.
SELECT name, salary * 12 AS annual_salary FROM employees;

-- Example result of: SELECT name AS full_name, salary AS monthly_salary FROM employees;
-- +---------------+----------------+
-- | full_name     | monthly_salary |
-- +---------------+----------------+
-- | Taro Tanaka   | 300000         |
-- | Hanako Suzuki | 280000         |
-- | Ichiro Sato   | 320000         |
-- +---------------+----------------+

The basic syntax for SELECT, AS, and DISTINCT is supported across all major databases.

SELECT name AS full_name, salary AS monthly_salary FROM employees;
SELECT DISTINCT department FROM employees;

In SQL Server, you can use TOP to limit the number of rows returned (equivalent to LIMIT in MySQL).

SELECT TOP 10 name, department FROM employees;

In PostgreSQL, DISTINCT ON (column) returns only the first row for each distinct value of the specified column.

-- Retrieves the highest-paid employee from each department.
SELECT DISTINCT ON (department) name, department, salary
FROM employees
ORDER BY department, salary DESC;

SELECT is the most frequently used statement in SQL and reads data from a table. Specifying only the columns you need reduces the amount of data transferred over the network and improves performance.

Aliases defined with AS can include non-ASCII characters, but be careful when referencing column names from application code — names that contain spaces must be wrapped in backticks (MySQL) or double quotes (standard SQL).

Use SELECT together with WHERE for filtering, ORDER BY for sorting, and LIMIT for limiting the number of rows returned.