MySQL内部联接查询给出三行

Question

Thanks for reading.

I'm trying to learn inner join and join. My aim is to comparing that if the user created the community is also marked as an admin in the CommunityMembers table (I'm not sure if INNER JOIN achieves this) and take all other community information from Community table related to CommunityID (this is possible with inner join as I understand).

I have two tables called Community and CommunityMembers.

the structure is for Community(it has other data such as date, contents etc...):

CommunityID -    Slug      - CreatedByUser
     1      -    video     -      2
     2      -    funny     -      2
     3      -    picture   -      4

for CommunityMembers

 CmID - UserID  -      Slug         - Power
   1  -   2     -      video        - admin
   2  -   2     -      funny        - admin
   3  -   4     -      picture      - admin

my php code: ( $_SESSION['UserID'] is 2 )

<?php

$sql = $dbc->prepare(" SELECT cm.*, com.* 
                       FROM Community com
                       INNER JOIN CommunityMembers cm ON cm.UserID = com.CreatedByUser
                       WHERE cm.UserID = '" . $_SESSION['UserID'] . "'");

$sql->execute();

if($sql->rowCount()){
    echo  $sql->rowCount();
    while($data = $sql->fetch()){
        $output .= $data['Slug'] .'<br />';
    }
    echo $output;
}else{
    $_ERROR = "no record";
}
?>

echo $output; prints

video
video
video
funny
funny
funny

and echo $sql->rowcount(); prints 6

Could you please help with this? Why is this printing same thing 3 times? and is my solution right to check if is user created the community is marked as admin in the CommunityMembers or do I need to check it?

Thanks.

Answer 1

Try this

$sql = $dbc->prepare(" 
SELECT cm.*, com.* 
FROM Community com
INNER JOIN CommunityMembers cm ON cm.UserID = com.CreatedByUser
WHERE cm.UserID = '" . $_SESSION['UserID'] . "'

GROUP BY com.CreatedByUser
");

Answer 2

$sql = $dbc->prepare(" SELECT DISTINCT cm.*, com.* 
                   FROM Community com
                   INNER JOIN CommunityMembers cm ON cm.UserID = com.CreatedByUser
                   WHERE cm.UserID = '" . $_SESSION['UserID'] . "'");

SELECT DISTINCT

http://dev.mysql.com/doc/refman/5.0/en/distinct-optimization.html

Answer 3

If all you need to know if its admin, don't bring all fields from CommunityMembers. Try this

$sql = $dbc->prepare(" SELECT DISTINCT cm.Power, com.*
                       FROM Community com
                       LEFT JOIN CommunityMembers cm ON cm.UseriID=com.CreaterByUser
                       WHERE cm.UserID = '" . $_SESSION['UserID'] . "'");

Didn't test it, but this should work even without DISTINCT.

Answer 4

If you select the 2 tables result SELECT cm.*, com.* it will return all differents couples so try to select only specifics fields you need.

PS : What is the full result, I mean not only the field slug ?