How can the use of array keys without quotes in PHP cause confusion and errors in SQL queries?

When using array keys without quotes in PHP, it can cause confusion and errors in SQL queries because SQL queries require string keys to be enclosed in quotes. To solve this issue, always enclose array keys in quotes when using them in SQL queries to ensure proper syntax and prevent errors. 

// Incorrect way that can cause confusion and errors in SQL queries
$array = ['id' => 1, 'name' => 'John'];
$sql = "SELECT * FROM users WHERE id = $array[id]";

// Correct way to enclose array keys in quotes to prevent errors in SQL queries
$sql = "SELECT * FROM users WHERE id = '{$array['id']}'";

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