尝试在简单的php系统中显示具有一对多关系的mysql数据？

Question

I have connected FirstPositionID/SecondPositionID with PositionID(PRIMARY KEY) from positions. Each positionID has one position name. Since i have 2 positions for players setted by position id, shouldn't php print position name of each id i have set? When i print PositionName it prints all positions i have inserted in my positions table. here is my tables

CREATE TABLE `players` (
`PlayerID` int(10) UNSIGNED NOT NULL,
`PlayerName` varchar(255) NOT NULL,
`CountryID` varchar(255) NOT NULL,
`FirstPositionID` int(11) UNSIGNED NOT NULL,
`SecondPositionID` int(10) UNSIGNED NOT NULL,
`Overall` int(11) UNSIGNED NOT NULL,
`Defence` int(11) NOT NULL,
`Speed` int(11) NOT NULL,
`Rebound` int(11) NOT NULL,
`Stamina` int(11) NOT NULL,
`TeamID` int(11) NOT NULL,
`Shooting` int(11) NOT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf16;

CREATE TABLE `positions` (
`PositionID` int(10) UNSIGNED NOT NULL,
`PositionName` varchar(255) NOT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf16;





//-----------php-----------------------

    $sql= "SELECT * from players,positions";
    $reg = mysqli_query($con,$sql);
    if(mysqli_num_rows($reg) > 0)
    {
        while($row = mysqli_fetch_assoc($reg))
        {
            echo "</br>Player:".$row['PlayerName']." Overall:".$row['Overall']." Position: ".$row['PositionName'];
        }

    }
    else 
    {
        echo "SQL error at: </br> ".$register."SYNTAX:</br>".mysqli_error($con)."</br>";
    }

RESULT:

Player:Agrabanis Overall:64 Position: Point Guard

Player:Athineou Overall:64 Position: Point Guard

Player:Agrabanis Overall:64 Position: Shooting Guard

Player:Athineou Overall:64 Position: Shooting Guard

Player:Agrabanis Overall:64 Position: Small Forward

Player:Athineou Overall:64 Position: Small Forward

Player:Agrabanis Overall:64 Position: Power Forward

Player:Athineou Overall:64 Position: Power Forward

Player:Agrabanis Overall:64 Position: Center

Player:Athineou Overall:64 Position: Center

Since i have set to firstplayer position ids 5,4 and to the secondplayer position ids 2,1 shouldnt just print Center,Power Forward(4,5 position ids) for first player and for secondplayer Shooting Guard,Point Guard(2,1 position ids)

Answer 1

please use left join or inner join instead of cross join and change your SQL string to something like

SELECT pl.PlayerName, pl.FirstPositionID, pl.Overall,
pl.SecondPositionID, po1.PositionName AS FirstPositionName,
po2.PositionName AS SecondPositionName FROM players pl
LEFT JOIN positions po1 ON(pl.FirstPositionID = po1.PositionID )
LEFT JOIN positions po2 ON (pl.SecondPositionID = po2.PositionID )
LIMIT 0,100

Also, change you while loop to

while($row = mysqli_fetch_assoc($reg)){
  echo "</br>Player:".$row['PlayerName']." Overall:".$row['Overall']." Position1: ".$row['FirstPositionName']." Position2:".$row['SecondPositionName '];
}

I think this will helps you...