Mysqli_select_db failed to connect to the database created by himself

$con = @ mysqli_connect ("localhost", "root", "", ") or die (" failed to connect to the database server ". Mysqli_connect_error ());
mysqli_select_db ("php_test", $con) or die ("specified database opening failed");

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Why my mysqli_select_db failed to connect to the database I created. Wrong path? I checked the file. That"s what it says. Ask experienced friends to share. Thank you

Mar.29,2021

parameter is used in reverse

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$con=mysqli_connect("localhost","root","password","php_test"); 
The

mysqli_connect () function directly selects the database.

MySQL Query : SELECT * FROM `codeshelper`.`v9_news` WHERE status=99 AND catid='6' ORDER BY rand() LIMIT 5
MySQL Error : Disk full (/tmp/#sql-temptable-64f5-1e47749-43712.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
MySQL Errno : 1021
Message : Disk full (/tmp/#sql-temptable-64f5-1e47749-43712.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
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