php - 如果数据库中不存在行如何返回零 PHP

Question

您好，我已经阅读了有关此问题的其他答案，但似乎无法让它为我工作。

我正在创建一个新表，但如果不存在行，我想将 0 放入变量中

下面的代码返回一个如下表:

 was_recalled  | total

它有空行。

在这种情况下我想要发生的事情是这样的

was_recalled    | total
Yes             |   0

这是我的代码:

<?php 
    $barPrelimSql = "select was_recalled, count(*) as total FROM mark_cards1 WHERE school = '$ownerSchool' AND was_recalled = 'Yes' AND competition_level1 = 'Prelim Champion' GROUP BY was_recalled";
    $barPrelimRes = mysqli_query($con,$barPrelimSql);

    while ($barPrelimRow=mysqli_fetch_array($barPrelimRes)){
        $barPrelimR = $barPrelimRow["total"];



        ?>

  var dataLace = google.visualization.arrayToDataTable([
      ['Placement', 'Recalled', 'Not Recalled'],
      ['Prelim Champs', <?php echo $barPrelimR; ?>, 5],
      ['Open Champs', 5, 24],
      ['Majors', 54, 44],

  ]);

        <?php } ?>

Answer 1

您在查询中使用了分组依据条件，这就是当查询中不存在行时它不会返回 0 计数的原因。

在我的建议中，您可以检查查询返回的行数，如果行数为零，则可以直接将其设置为 0。

<?php 
$barPrelimSql = "select was_recalled, count(*) as total FROM mark_cards1 WHERE school = '$ownerSchool' AND was_recalled = 'Yes' AND competition_level1 = 'Prelim Champion' GROUP BY was_recalled";
$barPrelimRes = mysqli_query($con,$barPrelimSql);
$row_count = mysqli_num_rows($barPrelimRes);
if($row_count > 0){
    while ($barPrelimRow=mysqli_fetch_array($barPrelimRes)){
        $barPrelimR = $barPrelimRow["total"];
        var dataLace = google.visualization.arrayToDataTable([
              ['Placement', 'Recalled', 'Not Recalled'],
              ['Prelim Champs', $barPrelimR, 5],
              ['Open Champs', 5, 24],
              ['Majors', 54, 44],

        ]);
    }
}
else{
    $barPrelimR = 0;
    var dataLace = google.visualization.arrayToDataTable([
          ['Placement', 'Recalled', 'Not Recalled'],
          ['Prelim Champs', $barPrelimR, 5],
          ['Open Champs', 5, 24],
          ['Majors', 54, 44],

    ]);
}

？>