Which kind of quote combination is preferred for MySQL queries in PHP?

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When inserting into MySQL with PHP, I can do either of the following:

$query = 'INSERT INTO tablename SET id = "4"';
$query = "INSERT INTO tablename SET id = '4'";
$query = 'INSERT INTO tablename SET id = \'4\'';
$query = "INSERT INTO tablename SET id = \"4\"";

Is there a reason (security, performance, code readability, ...) why I should prefer one of them?

asked 2 mins ago

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