php 连接 mysql

<?php
//<meta charset="utf-8">
//header('Content-Type: text/html;charset=utf-8');
$page = 1;
$datetime = '2019-09-07';

try {
    $conn = new mysqli('127.0.0.1', 'root', 'root,.','test');
}
catch (Exception $e) {
    die("数据库连接失败");
}

// mysqli_set_charset($conn,'utf8');
$conn->query("SET NAMES 'UTF8'");

$num_rec_per_page = 10;
$start_from = ($page-1) * $num_rec_per_page; 

// LIMIT $start_from, $num_rec_per_page
$sql="SELECT * FROM test where date_format(`datetime`, '%Y-%m-%d') = '$datetime' "; 


$rs=$conn->query($sql);

$codeArr = [];
if($rs->num_rows > 0) {
    // 输出数据
    while($row = $rs->fetch_assoc()){
        $tt = substr($row['datetime'], 0, 13);
        $codeArr[$tt] = $codeArr[$tt] ?? [];
        array_push($codeArr[$tt], $row['code']);
    }
}else {
    echo "暂无数据";
}

foreach ($codeArr as $key => &$value) {
    $value  = array_count_values($value);
}
unset($value);

print_r($codeArr);