mysqli左连接重复行

table com

id | com       | id_status  
1    testing 1   1  
2    testing 2   1  
3    testing 3   2  
4    testing 4   2  

table update

id_status | update  
1           update 1  
2           update 2  
3           update 3  


SELECT `update`.`update`, `com`.`com` as comen
FROM `update` 
    LEFT JOIN `com` ON `update`.`id_status`=`com`.`id_status`  

it results :

update 1  
testing 1  
update 1  
testing 2  
update 2  
testing 3  
update 2  
testing 4  

the update table results duplicate

i've done using group by update.id_status, it results :

update 1  
testing 1  
testing 2  
update 3  

the table com only resut 1 row

EDIT--
i got syntax from this MySQL LEFT JOIN display duplicate rows

$first = true;  
while($row = $query->fetch_object()){  
if($first){  
    echo $row->update;  
    $first = false;  
    echo "<br>";  
}  
echo $row->comen;  
echo "<br>";  
}  

update 1  
testing 1  
testing 2  
testing 3  
testing 4  

it fetch only 1 table row

i want the results looks like this :

update 1  
testing 1  
testing 2  
update 2  
testing 3  
testing 4  
update 3  
...  

--

how the right syntax work or maybe the query?

Try This, I think this will resolve:-

SELECT `update`.`update`, group_concat(`com`.`com`) as comen
FROM `update` 
    LEFT JOIN `com` ON `update`.`id_status`=`com`.`id_status` 
Group by `update`.`update`

and use your php as like:-

while($row = $query->fetch_object()){  
    echo $row->update;  
    $comen = explode(",", $row->comen);
    foreach($comen as $values){
     echo "<br>";  
     echo $values;
    }
    echo "<br>";  
} 

Use INNER JOIN instead of left join

SELECT `update`.`update`, `com`.`com` as comen
FROM `update` INNER JOIN `com` ON `update`.`id_status`=`com`.`id_status`; 

or can use DISTINCT keyword to avoid duplicate results

SELECT DISTINCT `com`.`id_status`, `update`.`update`, `com`.`com` as comen
FROM `update` LEFT JOIN `com` ON `update`.`id_status`=`com`.`id_status`;

According to your query , the result should have ok. Let have a look that the table com contain two value those id_status=1.

Now if you leftjoin com table with update table then the query will give 2 row corresponding id_status=1 because com table contain two row which id_status is 1.

if you want to get only any one row accroding to id_status then you have to use group by update.id-status or group by com.id-status

 SELECT `up`.`up`, `com`.`com` as comen FROM `up` LEFT JOIN `com` ON `up`.`id_status`=`com`.`id_status` group by up.id_status 

I used up instead of update because update is a keyword. Table:

Result: