"Tomorrow Graduation design reply, good nervous, beg each road moderator bless"

What I do is a graduation design topic system, now in the familiar code. I know which function is implemented by which code, but I am very vague about the specific meaning of the code. Looking for a master to help me in the next note in the rear ~ ~
Since my project is old based on modifying some of the added features, it is sometimes necessary to add

Extract ($_post);

Or

Extract ($_request);

To run some features, what does that mean?
Also, I have to follow a few sentences behind every code that executes the database.

$query = "SELECT * from $student _table where xuehao= ' $xuehao '"; mysql_query ("Set names ' GB2312 '"); $result =mysql_query ($ query); $row =mysql_fetch_array ($result);

And this is a part of revising the subject, I don't know what SN and ssn are for.

$query = "Select number as sn,surplus as SSN from $keti _table where id= ' $id '";   mysql_query ("Set names ' gb2312 '");   $result =mysql_query ($query); $row =mysql_fetch_array ($result), if ($number 1< $row [' SN ']) {if ($number 1< ($row [' SN ']-$row [' ssn ']) {echo "
the number of people can not be less than the number of selected topics, the number of changes failed! "; echo" 
    "; exit;} else{$query 2=mysql_query ("Update $keti _table set number= ' $newnumber ' where id= ' $id '"); $query 3=mysql_query ("Update $   Keti_table set surplus=surplus-($row [sn]-$newnumber) where id= ' $id ' "); mysql_query (" Set names ' gb2312 ' "); $result 1=mysql_query ($query 3);}} else{$query 4=mysql_query ("Update $keti _table set number= ' $newnumber ' where id= ' $id '"); $query 5=mysql_query ("Update $   Keti_table Set surplus=surplus+ ($newnumber-$row [SN]) where id= ' $id ' "); mysql_query (" Set names ' gb2312 ' ");   $result 2=mysql_query ($query 5); }if ($result ==true) {echo "
Modify the project success! ";   echo " 
    "; Exit }

This is a piece of code to download the material

$file _name= "related information. rar";  $file _dir= "temp/./";  if (!file_exists ($file _dir. $file _name))  {  echo "
The file could not be found
";  echo "
 
   ";  Exit;  }  else{  $file =fopen ($file _dir $file _name, "R");//Open File    Header ("Content-type:application/octet-stream");    Header ("Accept-ranges:bytes");    Header ("Accept-length:". FileSize ($file _dir. $file _name));    Header ("content-disposition:attachment; Filename= ". $file _name);  ReadFile ($file _dir. $file _name);  }

In particular, the last one on the "optional" and "not selectable" forms, do not understand

$surplus = ";  Extract ($_request);  $n =0;     if (empty ($offset))             {$offset =0;}    mysql_query ("Set names ' GB2312 '");  $where = (isset ($surplus) && strlen ($surplus) >0)? "Where surplus= ' $surplus '": '; Don't know  ... $query =mysql_query ("SELECT count (*) as SM from Keti $where");  $row =mysql_fetch_array ($query);  $count = $row [' SM ']; The total number of records      $query =mysql_query ("select * from Keti $where the ORDER by ID ASC limit $offset, $list _num") or Die ("fail");

Reply to discussion (solution)

Extract importing an array into the variable table (the association key is the variable name)

mysql_query ("Set names ' GB2312 '"); Used to notify MySQL of future interactions with the GB2312 character set
It's usually done once after connecting to the database.

By
if ($number 1< ($row [' SN ']-$row [' ssn ']) {
Echo

the number of people can not be less than the number of selected topics, the number of changes failed! ";
SN is an alternative number, SSN selected

No filter criteria Query
Select COUNT (*) as SM from Keti
Query with filter conditions
Select COUNT (*) as SM from Keti where surplus= ' $surplus '

Extract importing an array into the variable table (the association key is the variable name)

mysql_query ("Set names ' GB2312 '"); Used to notify MySQL of future interactions with the GB2312 character set
It's usually done once after connecting to the database.

By
if ($number 1< ($row [' SN ']-$row [' ssn ']) {
Echo

the number of people can not be less than the number of selected topics, the number of changes failed! ";
SN is an alternative number, SSN selected

No filter criteria Query
Select COUNT (*) as SM from Keti
Query with filter conditions
Select COUNT (*) as SM from Keti where surplus= ' $surplus '

This is the last sentence to understand

$where = (isset ($surplus) && strlen ($surplus) >0)? "Where surplus= ' $surplus '": ';
Ternary operations, equivalent to
if (Isset ($surplus) && strlen ($surplus) >0)) {
$where = "where surplus= ' $surplus '";
}else {
$where = ";
}

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