自动显示不在数据库中的日期的0销售额

Question

我使用Chart.js创建图表。我有一些日期和销售存储在数据库中。在这里，我使用ajax请求从数据库中选择记录，并通过将数据划分为两个不同的数组date["2017-12-18","2017-12-20","2017-12-26"]和amt["2000","3000","6000"]来使用该数据创建条形图：

$(document).ready(function(){
    $.post("ajax-req-handler.php",
    {
        key: "draw-line-chart"
    },
    function( data ){
        console.log(data);
        data = JSON.parse(data);
        var date = [];
        var amt = [];
        for(var i in data){     
            date.push(data[i].sale_date);
            amt.push(data[i].total);
        }
        console.log(date);
        console.log(amt);
        var ctx = document.getElementById("myChart").getContext('2d');
        var myChart = new Chart(ctx, {
            type: 'bar',
            data: {
                labels: date,
                datasets: [{
                    label: '',
                    data: amt,
                    backgroundColor: [
                        'rgba(255, 99, 132, 0.2)',
                        'rgba(54, 162, 235, 0.2)',
                        'rgba(255, 206, 86, 0.2)',
                        'rgba(75, 192, 192, 0.2)',
                        'rgba(153, 102, 255, 0.2)',
                        'rgba(255, 159, 64, 0.2)'
                    ],
                    borderColor: [
                        'rgba(255,99,132,1)',
                        'rgba(54, 162, 235, 1)',
                        'rgba(255, 206, 86, 1)',
                        'rgba(75, 192, 192, 1)',
                        'rgba(153, 102, 255, 1)',
                        'rgba(255, 159, 64, 1)'
                    ],
                    borderWidth: 1
                }]
            },
            options: {
                scales: {
                    yAxes: [{
                        ticks: {
                            beginAtZero:true
                        }
                    }]
                }
            }
        });
    });
});

这是我的ajax-req-handler.php

$sql = "SELECT DATE(sale_date) AS sale_date, SUM(total) AS total FROM customers GROUP BY DATE(sale_date)";
        $result = $conn->query($sql);
        $db_data = array();
        while ($row = $result->fetch_assoc()) {
            $db_data[] = $row;
        }
        echo json_encode($db_data);

everuthing工作正常，但我想要的是显示没有任何销售的日期0值。 20至26和18至20之间的日期值应为0

Answer 1

您需要使用COALESCE

$sql = "SELECT DATE(sale_date) AS sale_date, COALESCE(SUM(total),0) AS total FROM customers GROUP BY DATE(sale_date)";

你需要更改php代码（因为你想要的那些日期也不在表格中，而是介于你实际从表中获得的日期之间）： -

$db_data = array(); //change from this line onward
while ($row = $result->fetch_assoc()) {
  $db_data[$row['sale_date']] = $row;
}
$date_array = array_keys($db_data);

$begin = new DateTime($date_array[0]);
$end = new DateTime(end($date_array));

$daterange = new DatePeriod($begin, new DateInterval('P1D'), $end);

$actual_array = [];
foreach($daterange as $date){
    if(isset($db_data[$date->format("Y-m-d")])){
        $actual_array[] = ['sale_date'=>$date->format("Y-m-d"),'total'=>$db_data[$date->format("Y-m-d")]['total']]; 
    }else{
        $actual_array[] = ['sale_date'=>$date->format("Y-m-d"),'total'=>0];
    }
}
if(isset($db_data[$end->format("Y-m-d")])){
    $actual_array[] = ['sale_date'=>$end->format("Y-m-d"),'total'=>$db_data[$end->format("Y-m-d")]['total']];   
}else{
    $actual_array[] = ['sale_date'=>$end->format("Y-m-d"),'total'=>0];
}
echo json_encode($actual_array);