How to get unique field values ​​based on another field?

Question

SQL

Suppose there is a table with three fields id, product and color, product stores product types and color stores their colors, for example, product stores ten lighthouses and five sweaters, and color has 7 unique colors belonging to T-shirts (sweaters are not important), how to get all unique colors related to jerseys

Answer 1

<?php

$product = 'sweater';
$query = "select distinct color from products where product = ?;";

// get DB version using PDO
$stmt = $pdo->prepare($query);
$stmt->execute([$product]);
$colors = $stmt->fetchAll(PDO::FETCH_ASSOC);

print_r($colors);

PHP PDO online test

Answer 2

DISTINCT or GROUP BY will help you:
SELECT DISTINCT color FROM TableName;
SELECT color FROM TableName GROUP BY color;
The first option is more convenient for me.