MySQL select rows from exactly 7 days ago

问题:

I'm completely stumped on this one, being trying for hours but with no success, hoping someone can help. Trying to build a cron script to run daily that returns the rows that are exactly 7 days older than the current date.

The thing is, my query is not returning anything. No error messges, nothing (I know there are entries in the DB from the last 7 days - we get about 7000 new entries a day, so they are there!) I've tried a SELECT * and echo out the edit date with success, so everything is working, apart from my SQL script.

The column I'm referencing (edit_date) is type 'datetime' formated with Y-m-d h-m-s. This column always has a datetime value assigned on both create and edit.

function get_ad_sql($table){
    $sql = "SELECT 
                * 
            FROM 
                ".$table." 
            WHERE 
                edit_date = DATE_SUB(NOW(), INTERVAL 7 DAY)
            ";  
    return $sql;
}

And calling the function and 'trying' to echo the primary_key:

$sqlAng = get_ad_sql('angebote');
$result = mysql_query($sqlAng);
while($row = mysql_fetch_array($result)){
    echo $row['primary_key'];
}

I've tried every variation of DATE_SUB(NOW(), INTERVAL 7 DAY), including CURDATE(), DATE_FORMAT(edit_date, '%m/%d/%Y') that I could find on here and online, but couldn't get anything to work. Hope someone can help me!

回答1:

It is very rare to get same datetime entries which gives date and time upto seconds. Therefore, for getting appropriate results we need to ignore the time part, and deal with date part, thus, using CURDATE() function.

You could do that ignoring the time part and compare with the date using following:

function get_ad_sql($table){
    $sql = "SELECT 
                * 
            FROM 
                ".$table." 
            WHERE 
                DATE(edit_date) = DATE_SUB(CURDATE(), INTERVAL 7 DAY)
            ";  
    return $sql;
}

回答2:

NOW() returns DATETIME value, you should use a DATE function to get date without time, e.g. -

SELECT * FROM table WHERE edit_date = DATE_SUB(DATE(NOW()), INTERVAL 7 DAY);

If type of edit_date field is DATETIME, then this field should be wrapped by DATE() function too -

SELECT * FROM table WHERE DATE(edit_date) = DATE_SUB(DATE(NOW()), INTERVAL 7 DAY);

回答3:

Your script is working... I highly doubt you have something exactly 7 days ago (to the second).

Perhaps you wanted something WHERE edit_date>DATE_SUB(NOW, INTERVAL 7 DAY) AND edit_date<DATE_SUB(NOW, INTERVAL 6 DAY)?

Or, if you want to compare just the date (not the time) portions, compare the output of DATE() instead.

回答4:

 SELECT SUBDATE(CURDATE(), 7)

Try this.