What is the difference between using "$sql = ..." and "mysql_query(...)" in PHP?

When using "$sql = ...", you are simply assigning a SQL query string to a variable. However, to execute the query and interact with the database, you need to use functions like "mysql_query(...)". This function sends the query to the database and returns a result resource that can be used to fetch data or perform other operations.

$sql = "SELECT * FROM users";
$result = mysql_query($sql);