PHP双while循环，第二个循环只运行一次

根据您的代码判断，有太多未知因素无法解决问题。

但我在代码中写了一些注释，指出了潜在的问题/调试建议：

// what are the (expected) values of $nextDate and $currentDate ?
while ($nextDate < $currentDate) {
    $nextDate = date('Y-m-d', strtotime('+ 6 days', strtotime($weekDate)));
    // this makes the big loop either run once (if $weekDate is within the 6 days interval)
    // or an infinite loop if it isn't
    $qM =   "select count(*) as count ,Deposit.DepositNo, Deposit.DepositDate,
             sum(DepositItem.Amount) as Amount,DAmount
             from DepositItem
             inner join Deposit on Deposit.DepositNo=DepositItem.DepositNo
             where Deposit.DepositDate>='" . $weekDate . "' and Deposit.DepositDate<='" . $nextDate . "' group by Deposit.DepositNo 
             order by Deposit.DepositNo desc";
    // do an echo $qM and copy it in Phpmyadmin, see if it returns expected results
    $connM = new dbconfig(); // not quite good to have these inside a loop
    $connM->connectdb(); // you should put these 2 lines outside
    $connM->execute($qM);
    $amt = 0;
    $damt = 0;
    while ($rowsM = $connM->fetch_row()) { // do a var_dump($rowsM) inside the loop
        $amt = $amt + $rowsM['Amount'];
        $damt = $damt + $rowsM['DAmount'];
    }
}

$nextDate总是大于$currentDate，因为您要添加6天

$nextDate=date('Y-m-d',strtotime('+ 6 days',strtotime($weekDate)));