如果数据中有“在……期间使用"项，则用复合键选择项. [英] select item with composite key if there are items in data "using while"

问题描述

大家好
我想知道当我拥有复合主键时如何从数据库中选择项目

我有这张桌子
sID    cID    item1
1)
当sID和cID是复合主键时
而item1是我要选择的

而且我也想使用此代码选择每个项目(如果有项目的话)

hi every one
I want know how I can select item from database when I have composite primary key

I have this table
sID      cID      item1
 1       cs9        rr

when sID &cID are composite primary key
and item1 is what I want to select

and also I want use this code to select every items if there are items

<?php
$db_name="grade_book";
        $tbl_name="students_course";
        mysql_connect("localhost", "root", "");
        mysql_select_db("$db_name");
$sID=$_SESSION['sID'];
        $sql=mysql_query("SELECT * FROM course WHERE cID in(SELECT cID FROM $tbl_name WHERE sID=$sID)") or die(mysql_error());
        while($mysqlf =mysql_fetch_array($sql))
        {
            $chrs=$mysqlf['chrs'];
            //echo"$sid<br>";
            echo "$chrs<br>";

        }
?>

>>>我知道此选择错误

>>>> I know this select is wrong

推荐答案

db_name = " ;

db_name="grade_book";

tbl_name = 学生课程"; mysql_connect(" ，" root"， ")； mysql_select_db("

tbl_name="students_course"; mysql_connect("localhost", "root", ""); mysql_select_db("

db_name" );

db_name");

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