从存在ID（从另一表）的一个表中选择

Question

First of all, I'd just want to say that I'm sorry for the poor title. I'm really struggling with explaining the problem I'm facing in just a short sentence.

I have a table called actors which contains an aID (primary key) and an aName and some more stuff. I also have a table called videos which contains vID (primary key) and other data. The third and last table I have is called connections and that one contains a primary key, a cVideoID and a cActorID .

Let's say I have created a video and when I navigate to the video *www.example.com/video.php?v=primary_key* I'd like to print out all actors who are in that movie (actor1, actor2, actor3 and actor4). Therefor I created the connections -table to keep track of all movie-actor connections. For every movie I create I connect the actors with the movie.

I thought that I could do something like this:

<?php
    $result2 = mysql_query("SELECT `actors`.`aID`, `actors`.`aName` FROM `actors` WHERE `connections`.`cVideoID` = {$_get['v']}");
    while($actors = mysql_fetch_array($result2))
    {
        echo "<a href='actor.php?id={$actors['aID']}>{$actors['aName']}</a> ';
    }
?>

But it seems like that's not working. Any ideas?

Answer 1

What you want to do, is select all of the entries from connections , where the video ID is the selected video. Then, you JOIN on the actors table, to get all of the information about the actors that were found.

Example: Get all of the actor's names for a specific video ID:

SELECT a.aName 
FROM connections c 
  LEFT JOIN actors a 
  ON a.aID = c.aID 
WHERE c.vID = 1;

SQL Fiddle

Answer 2

What you need here is a join. A normal left join works like this:

LEFT JOIN [name of table] [name of table you will want to use] 
       ON ([where statements searching for the right columns to join]) 

So your query will look something like this:

   SELECT a.aID, a.aName 
     FROM `connections` c 
LEFT JOIN `author` a ON (c.cActorID=a.aID) 
    WHERE c.cVideoID=[id of the video]

Now first of all you say the database you want to catch the columns aID and aName from the table a next you use the FROM statement to "import" the connections table as "c". You then load the author table and make it accessible as "a" (see the select statement a.[...]) and you also say that it should join the two tables ON every c.cActorID=a.aID and in the end you make a where statement to declare you are only searching for videos with the c.cVideoId=[id]