这样写的MySQL函数输出什么？

Question

I've ordered a project from a developer, and I'm trying to fix the errors I find along the way.

One is a MySQL query with the DATE_FORMAT() function, that makes the query not return anything.

SELECT * FROM food_cart 
WHERE cart_userId='3' 
AND cart_itemId='8' 
AND date_format(cart_date,'%Y-%m-%d %H')='".date("Y-m-d")."'

The code seems to be correctly formatted, as it does not return an error when executed in phpMyAdmin. It does however, not return anything.

The table looks like this:

I think it is supposed to try to look at just the date (i.e. 2011-10-07) and not the exact time, as it is not relevant for the query. I'm just a beginner at MySQL and I'm not quite sure what I'm doing here.

Any help appreciated!

Mike.

Answer 1

As requested, here's my version of Johan's answer:

$date = date( "Y-m-d", $timestamp );
$sql = "SELECT * FROM food_cart
        WHERE cart_userId = '3' 
          AND cart_itemId = '8' 
          AND cart_date >= '$date'
          AND cart_date < '$date' + INTERVAL 1 DAY"; 

This query will

• make full use of an index on cart_date,
• make full use of the query cache, and
• return exactly those rows for which the date part of cart_date equals $date.