我沒有從下面的代碼中得到所需的結(jié)果。一切正常，但有一個主要問題：當(dāng)數(shù)據(jù)庫中沒有歌曲時，它僅通過后退按鈕顯示空結(jié)果。它無法顯示回聲“抱歉！” 我們的數(shù)據(jù)庫中沒有這首歌。我不知道錯誤在哪里。所以請幫忙。提前致謝?。。?lt;?php// Php code that fetches audio from the database in server and shows the audio files with singers available for the submitted data// In submission page DROPDOWN consists of Playlist name and TEXTBOX allows to type the song number for that playlist.// Standard format for the audio file stored in the databse is Songnumber-Playlistname-Singer's Shortname.mp3// MP3 files will be inside the AUDIO folder and this PHP code runs from the root folder where there is index.html file for data submission.// Valid song Numbers of Each Playlists that user choose$validsongnumbers = [    'Rock' => 3,     'Pop' => 5,     'Jazz' => 6];// Data captured from dropdown submitted by a user in homepage $PlaylistName = $_POST['Dropdown'];$songNumber = $_POST['songnumber'];// Check the playlist existsif (!array_key_exists($PlaylistName, $validsongnumbers)) {    echo 'Invalid playlist provided.';    exit;}// Check the song number is not greater than what is allowedif ((int)$songNumber > $validsongnumbers[$PlaylistName]) {    echo  'Invalid song number provided.';    exit;}