如何在PHP中使用数据聚合函数

//连接数据库
$conn = mysqli_connect("localhost", "root", "", "testdb");
//SELECT COUNT(*) AS total FROM students
$sql = "SELECT COUNT(*) AS total FROM students";
$result = mysqli_query($conn, $sql);
if(mysqli_num_rows($result) > 0) {
    while($row = mysqli_fetch_assoc($result)) {
        echo "学生表中总共有 ".$row['total']." 条记录。";
    }
}

//SELECT SUM(score) AS score_total FROM students
$sql = "SELECT SUM(score) AS score_total FROM students";
$result = mysqli_query($conn, $sql);
if(mysqli_num_rows($result) > 0) {
    while($row = mysqli_fetch_assoc($result)) {
        echo "学生表中成绩总和为：".$row['score_total']." 分。";
    }
}

//SELECT AVG(score) AS score_avg FROM students
$sql = "SELECT AVG(score) AS score_avg FROM students";
$result = mysqli_query($conn, $sql);
if(mysqli_num_rows($result) > 0) {
    while($row = mysqli_fetch_assoc($result)) {
        echo "学生表中成绩平均分为：".$row['score_avg']." 分。";
    }
}

//SELECT MAX(score) AS max_score FROM students
$sql = "SELECT MAX(score) AS max_score FROM students";
$result = mysqli_query($conn, $sql);
if(mysqli_num_rows($result) > 0) {
    while($row = mysqli_fetch_assoc($result)) {
        echo "学生表中成绩最高分为：".$row['max_score']." 分。";
    }
}

//SELECT MIN(score) AS min_score FROM students
$sql = "SELECT MIN(score) AS min_score FROM students";
$result = mysqli_query($conn, $sql);
if(mysqli_num_rows($result) > 0) {
    while($row = mysqli_fetch_assoc($result)) {
        echo "学生表中成绩最低分为：".$row['min_score']." 分。";
    }
}