MySQL插入语句不会插入？

Question

I have attached my PHP code below. It calculates the cumulative value correctly and builds the SQL statement correctly (tested by echo $sql; ). However, the instert statement into MySQL is unsuccessful. Any ideas?

<?php 
ini_set('memory_limit', '500M');
set_time_limit(1800);
$dbh = new mysqli('localhost','user','password','database') or die(mysql_error());
$query = "SELECT * FROM table1 ORDER BY id, date";
$del = "DELETE FROM table2";
$dbh->query($del);
if ($dbh->multi_query($query)){
    if ($result = $dbh->store_result()){
        $id = 0;
        while ($row = $result->fetch_row()){
            $date = $row[0];
            $cvalue = $row[2];
            $id = $row[1];
            $cumulative = 0;
            // Pull most recent cumulative value 
            $sql_recent = "SELECT * FROM table2 WHERE id = $id ORDER BY date DESC LIMIT 1";
            if ($dbh->multi_query($sql_recent)){
                if ($result_recent = $dbh->store_result()){
                    while ($row_recent = $result_recent->fetch_row()){
                        if($row_recent[0] != $date){
                            $cumulative = $row_recent[2];
                        }
                    }
                }
            }
            $cumulative += $cvalue;
            $sql = 'INSERT INTO table2 (id, date, cumulative) VALUES (';
            $sql .= "'".$row[1]."',";
            $sql .= "'".$date."',";
            $sql .= "'".$cumulative."',";
            $sql .= ')';
            $dbh->query($sql);
            echo $sql;
        }
    }
}
$dbh->close();
?>

Answer 1

You have an extra comma after the last value:

$sql .= "'".$cumulative."',";

Try removing that:

$sql .= "'".$cumulative."'";

Answer 2

$ cumulative之后的逗号将使语法错误。