Simple code to answer, the younger brother really do not understand why return failed! What to do with it

Simple code to answer, the younger brother really do not understand why return failed!
I want to add data to the database, can fail, this is my SQL class, and then down the code is I call this class of code, I hope the good-hearted people to help answer, grateful!
Class sqltool{
Private $conn;
Private $host = "localhost";
Private $user = "root";
Private $password = "root";
Private $db = "Test";

function SqlTool () {
$this->conn=mysql_connect ($this->host, $this->user, $this->password);
if (! $this->conn) {
Die ("Connect faild!". Mysql_error ());
}
mysql_select_db ($this->db, $this->conn);
mysql_query ("Set names GBK");
}
Complete Select
function Execute_dql ($sql) {

//}
Function:update, Delete,insert
function Execute_dml ($sql) {
$b =mysql_query ($sql);
Var_dump ($b);
if (! $b) {
Return 0;//faild
}else{
if (Mysql_affected_rows ($this->conn) >0) {
Return 1;//success
}else{
Return 2;//no Influence
}
}
}
}
?>





Require_once "mysqltool.php";
Create MySQL
$sql = "INSERT INTO User1 (name,password,email,age) VALUES (' Xiao Ming ', MD5 (123), ' xiaoming@sina.com ', 20)";
$sqlTool =new SqlTool ();
$res = $sqlTool->execute_dml ($sql);
Var_dump ($res);
if ($res ==0) {
echo "faild!";
}else if ($res ==1) {
echo "Success";
}else if ($res ==2) {
echo "no influence";
}
?>







------Solution--------------------
Failure must have been the failure of SQL command execution.

$b =mysql_query ($sql) or Die (Mysql_error ());
This way, you will be prompted if there is an error.

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