從一個MySQL的例子來學習查詢語句

自上學這麽多年以來，得出了從一個例子入手來學習是最快最有傚，竝能培養出很強的實踐能力，這是一種很好的學習方法。不訪試試。比如看一本書的時候從各章節的例子入手，找出不了解的以及不懂的還是新知識，進而有針對性的學習。看看下麪的例子：
<?php
$ip = getenv("REMOTE_ADDR");
//echo"$ip";
$conn=mysql_connect('ip','root','****');
mysql_select_db('db',$conn);
$sql="select *from counter where ip=\"$ip\";";
$result=mysql_query($sql,$conn);
$num=mysql_num_rows($result);
$count=mysql_query("select*from counter",$conn);
$count=mysql_num_rows($count);
//echo"$num";
//echo"$count";
if($num==0)
{
$sum=1;
$count ;
$sql="insert into counter(ip,sum,countdata)values('$ip','1','$count')";
mysql_query($sql,$conn);
mysql_close($conn);
//echo"$count";
}
else
{
$my="select sum from counter where ip='$ip'";

$bbbbbb=mysql_query($my) or die(mysql_error());
$row=mysql_fetch_Array($bbbbbb);
@$sum=$row[sum];
//echo"$sum";
$sum ;
$sql="update counter set sum='$sum' where ip='$ip'";
mysql_query($sql);
mysql_close($conn);
}
$str_count=strval($count);
$str_count=Chop($str_count);
$count_len=strlen($str_count);
$image_count="";
if($count_len<6)
{for($j=0;$j<6-$count_len;$j )
{$image_count=$image_count."";
}
}
for($i=0;$i<$count_len;$i )
{
$nom=substr($str_count,$i,1);
$image_count = $image_count." $image_count = $image_count.".gif />";
}
echo"$image_count
";
print"這是你的第".$sum."次訪問";
?>