Question

I have a problem with group_concat in mysql query :

It stops on 513 number !

This is the normal query and it returns 813 rows :

SELECT * 
FROM survey_votes
WHERE sid =  '4'

and now the problem is with this query:

SELECT s.*,     
    GROUP_CONCAT(v.oid) AS myoids
    FROM survey s
    LEFT JOIN survey_votes v ON s.sid=v.sid
    WHERE s.sid='4'

This returns 1 row containing an array ‘myoids’ up to 513 strings.

strucutr of table ‘survey’:

sid  int(11)          
stitle   varchar(255)
sdesc    text     
soptions text    
sdate    datetime  
active   int(1)

survey_votes:

vid int(11) 
sid int(11)     
uid int(11)     
uip varchar(255)    
oid int(11)     
sdate   datetime

myoids only contains upto 513 rows :

Array
(
    [0] => 1
    [1] => 1
    [2] => 3
    .........
    [511] => 1
    [512] => 
)

Answer 1

This is because MySQL truncates the result of GROUP_CONCAT after a certain limit:

The result is truncated to the maximum length that is given by the
group_concat_max_len system variable, which has a default value of
1024.

Try increasing the value of group_concat_max_len variable using the SET command:

SET SESSION group_concat_max_len = 1024 * 1024; -- 1MB