while循环以更新数据库中的日期仅更新第一行？

Question

I have no idea why this won't work.

function query($sql) {


     $this->result = @mysql_query($sql, $this->conn);

     return($this->result != false);

}


function convert() { $this->db->open(); $sql_update = ""; $this->db->query("SELECT * FROM ACCOUNTS "); $str = ''; while ($row = $this->db->fetchassoc()) { $jobNum = $row['JOBNUMBER']; $old_date = $row['INSTALLDATE']; $new_date = date("Y-m-d", strtotime($old_date)); $sql_update = "UPDATE ACCOUNTS SET INSTALLDATE='$new_date' WHERE JOBNUMBER='$jobNum' "; //$this->db->query($sql_update) or die($this->response->throwResponseError(MSG_DATABASE_ERROR . mysql_error())); $str .= $jobNum . " -- " . $new_date . "
"; }

    return $str;
}

If I run it with that line commented out, it returns all the results i want. But when I uncomment the line where it actually runs the update, it updates the first record and stops the loop. Why?

Answer 1

When you run update, it invalidates the hidden statement hander in your db and the results associated with it.

db->query("SELECT …") -- creates the handler

-- 1st iteration
db->fetchassoc() -- fetches the first row
db->query("UPDATE …") -- creates another handler and destroys the old one

-- 2nd iteration
db->fetchassoc() -- no rows returned by `UPDATE`, nothing to fetch

What you are trying to do, can be done more easily using a single statement:

UPDATE  accounts
SET     installed = DATE_FORMAT(STR_TO_DATE(installed, @current_format_string), '%Y-%d-%m')

, where @current_format_string is how your dates are formatted now.

Update:

Try running this query:

UPDATE  accounts
SET     installdate = DATE_FORMAT(STR_TO_DATE(installdate , '%m/%d/%Y'), '%Y-%d-%m')

Before you run UPDATE query, you may want to check the results with SELECT :

SELECT  DATE_FORMAT(STR_TO_DATE(installdate, '%m/%d/%Y'), '%Y-%d-%m')
FROM    accounts