PHP mysqli_query不返回混合数据类型，varchar和decimal

Question

我有一个执行查询的函数，然后创建一个JSON。它工作得很好

function getStmtJson($conn){
$sth = mysqli_query($conn, "SELECT firstname, lastname FROM users");
$rows = array();
while($r = mysqli_fetch_assoc($sth)) {
    $rows[] = $r;
}
print json_encode($rows);

}

这是返回值：

[{"firstname":"Lena-Jill","lastname":"Grottburg"},{"firstname":"Rafael"...]}

但是，当我将SQL输入更改为：

时

SELECT name, latitude, longitude FROM analysis GROUP BY name, latitude, longitude

我没有得到任何回报。 该查询在phpmyadmin中工作正常。

在表格中，name的类型为varchar，纬度和经度为十进制。

如果从查询中删除了名称，那么它就能正常工作。

编辑：

完整的PHP代码：

$servername = "localhost";
$username = "username";
$password = "password";
$dbname = "robin";

$input = "get_spots";

$case_one = "get_spots";
$case_two = "input_analysis";

$conn = new mysqli($servername, $username, $password, $dbname);
if ($conn->connect_error) {
    die("Connection failed: " . $conn->connect_error);
}

if(strcmp($input, $case_one) == 0){
    getStmtJson($conn);
    echo "<br> <br>";
    getSpotList($conn);
}
elseif(strcmp($input, $case_two) == 0){
    echo "case_two";
}
else{
    echo "else";
}

$conn->close();

function getStmtJson($conn){
    $sth = mysqli_query($conn, "SELECT firstname, lastname FROM users");
    $rows = array();
    while($r = mysqli_fetch_assoc($sth)) {
        $rows[] = $r;
    }
    print json_encode($rows);
}

function getSpotList($conn){
    $sth = mysqli_query($conn, "SELECT name, latitude, longitude FROM analysis GROUP BY name, latitude, longitude");
    $rows = array();
    while($r = mysqli_fetch_assoc($sth)) {
        $rows[] = $r;
    }
    print json_encode($rows);
}