SELECT

SELECT is the most important statement in SQL. It is how you retrieve data from your database. Everything else — inserts, updates, deletes — is just maintenance. SELECT is where you get the answers to your questions.

Selecting All Data

To get every row and every column from a table:

SELECT * FROM students;

The * means "all columns." This is great for exploring a table but not practical for large tables with millions of rows.

Selecting Specific Columns

Most of the time, you only need certain columns:

SELECT first_name, last_name, email FROM students;

This is faster and cleaner. Only fetch the data you actually need.

Column Aliases

You can rename columns in your results using AS:

SELECT
  first_name AS "First Name",
  last_name AS "Last Name",
  email AS "Email Address"
FROM students;

This is useful when you want friendlier column names in your results, especially when building reports or feeding data to an application.

Filtering with WHERE

Use WHERE to filter rows:

SELECT first_name, last_name
FROM students
WHERE enrollment_date > '2023-01-01';

Only students who enrolled after January 1, 2023 will be returned. We will cover more filtering options in the WHERE lesson.

Sorting with ORDER BY

Sort your results:

SELECT first_name, last_name, date_of_birth
FROM students
ORDER BY date_of_birth DESC;

ASC sorts ascending (smallest first) and DESC sorts descending (largest first). ASC is the default.

Limiting Results

When working with large tables, you often want just the first few rows:

SELECT first_name, last_name
FROM students
ORDER BY enrollment_date DESC
LIMIT 10;

This gives you the 10 most recently enrolled students. You can also use OFFSET to skip rows:

SELECT first_name, last_name
FROM students
ORDER BY enrollment_date DESC
LIMIT 10 OFFSET 20;

This skips the first 20 and returns the next 10. Useful for pagination.

Removing Duplicates

Use DISTINCT to eliminate duplicate rows:

SELECT DISTINCT last_name
FROM students
ORDER BY last_name;

This returns each unique last name only once, regardless of how many students share it.