Write a generic class that connects to the database, and SQL statement execution has a problem

wrote a generic class to connect to the database, the SQL statement was executed with a problem
There are two files in sqltool.php and Connector-test.php,sqltool code as follows:
Class SqlTool
{
Private $conn;
Private $host = "localhost";
Private $user = "root";
Private $password = "root";
Private $db = "DB1";

function SqlTool ()
{
$this->conn=mysql_connect ($this->host, $this->user, $this->password);
if (! $this->conn)
{
Echo ("Database Not Connected");
}
mysql_select_db ($db, $this->conn);
mysql_query ("Set names UTF8");
}
function Execute_dml ($sql)
{
$b =mysql_query ($sql, $this->conn);
if (! $b)
{
return 0;
}
Else
{
if (Mysql_affected_rows ($this->conn) >0)
{
return 1;
}
Else
{
return 2;
}
}

}
}
?>
The code for Connector-test is as follows:
Require_once "sqltool.php";

$sql = "INSERT INTO table1 values (5, ' 187388 ', ' op ')";
$st =new SqlTool ();
$res = $st->execute_dml ($sql);
if ($res ==0)
{
echo "Execution unsuccessful";
}
else if ($res ==1)
{
echo "Successful execution";
}
else if ($res ==2)
{
echo "No row count effect";
}
?>
Now running connector-test.php, always shows that execution is unsuccessful and does not know what the reason is. Hope Master Enlighten. The system is FEDORA15.

------Solution--------------------
SQL command is wrong!

Since you want to encapsulate database operations, you need to take all the circumstances into account
Mostly encapsulation error handling
------Solution--------------------

PHP Code

#SqlTool. php ... $b =mysql_query ($sql, $this->conn); #加一句: if (! $b)     
Error-->>: ". Mysql_error ());  If an error occurs, all the SQL statements and MySQL errors are called out ...
------Solution--------------------
A successful insert may have been performed

Later inserts because 5 is the primary key value, failed, to print out an error such as # #. Come on...... Encapsulates the re-write frame
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