now() or date(y-m-d) doesn't work when trying to query using php and sql to a mysql database : I'm trying to check to see if one date (in my database) is larger (later) then the current date. I've looked on other questions for a solution but none of them seem to work.

    $sql = "SELECT * FROM customer_details, rental_details WHERE customer_details.customer_ID = rental_details.customer_ID AND rental_details.date_return >= date('y-m-d')";

Ive also tried

    $sql = "SELECT * FROM customer_details, rental_details WHERE customer_details.customer_ID = rental_details.customer_ID AND rental_details.date_return >= now()";

Ive tried every combination of parentheses and brackets with these two, nothing seems to work.

Any suggestions?
This is not a duplicate question, I've looked all over stack overflow. 