you can use substring_index(group_concat(column),’,',2). it will return the first 2 concated values.

tblmovies
MovieId MovieName
1 The Take
2 Fatal Contact
3 Flashbacks of a Fool
4 Teddy Bear
5 Nanking

tblgenres
GenreId GenreName
1 Action
2 Horror
3 Sci-Fi
4 Documentary
5 Drama
6 History

tblmovie_genres
movieId GenreId
1 2
1 4
1 5
2 4
4 5
3 5
5 6

When I was selecting the Movie whith Id 1 GROUP_CONCAT will result Horror,Documentary, Drama ; But I want to get only 2 genres which is Horror,Documentary.

Please somebody help me .

Thanks.

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. The value can be set higher, although the effective maximum length of the return value is constrained by the value of max_allowed_packet. The syntax to change the value of group_concat_max_len at runtime is as follows, where val is an unsigned integer:

SET [GLOBAL | SESSION] group_concat_max_len = val;

Current values in Our server

max_allowed_packet = 67107840
group_concat_max_len = 1024

Query:

To how much extent ,I can increase this variable size .and what is the maximumm data limit of GROUP_CONCAT

SELECT DISTINCT(md.id), (SELECT GROUP_CONCAT(categories.category SEPARATOR ‘, ‘) AS category FROM member_categories LEFT JOIN categories ON member_categories.category_id = categories.id WHERE member_categories.member_id = md.id) AS category FROM member_directory md LEFT JOIN member_categories mc ON md.id = mc.member_id LEFT JOIN categories ON mc.category_id = categories.id WHERE mc.category_id IN (138) GROUP BY md.name ORDER BY md.isfeatured DESC, RAND(1283945655) LIMIT 0, 10
====================================================================
id | category |
——————————————————————–
2275 | VACATION RENTALS, MASSAGE THERAPY, CONDOMINIUMS |
1388 | VACATION RENTALS |
1839 | VACATION RENTALS, CONDOMINIUMS |
1845 | CONDOMINIUMS, VACATION RENTALS |
1808 | REALTORS, VACATION RENTALS |
1899 | CONDOMINIUMS, VACATION RENTALS |
951 | CONDOMINIUMS, VACATION RENTALS |
1713 | VACATION RENTALS, CONDOMINIUMS |
2240 | TRAVEL AGENCIES, VACATION RENTALS |
2285 | VACATION RENTALS, CONDOMINIUMS |
====================================================================

However, if anyone has any tips to make this better, please post! Thanks!

SELECT DISTINCT(md.id),GROUP_CONCAT(categories.category SEPARATOR ‘, ‘) AS category FROM member_directory md LEFT JOIN member_categories mc ON md.id = mc.member_id LEFT JOIN categories ON mc.category_id = categories.id GROUP BY md.name ORDER BY md.isfeatured DESC, md.name ASC LIMIT 0, 10
====================================================================
id | category |
——————————————————————–
951 | CONDOMINIUMS, VACATION RENTALS |
1711 | VACATION RENTALS, REALTORS |
1413 | VACATION RENTALS |
1163 | BOATING/FISHING/MARINE |
2034 | VACATION RENTALS |
2240 | TRAVEL AGENCIES, VACATION RENTALS |
2033 | APARTMENT/HOUSE RENTALS |
2208 | APARTMENT/HOUSE RENTALS |
2153 | HEARING AIDS, MEDICAL SERVICES/HOSPITALS/CLINICS, AUDIOLOGY |
1002 | CONDOMINIUMS |
====================================================================

If I add any conditions regarding the category, the GROUP_CONCAT starts returning only the category mentioned in the WHERE clause (I don’t think I explained that very well, but here is an example). Adding a WHERE clause to the query:
SELECT DISTINCT(md.id), GROUP_CONCAT(categories.category SEPARATOR ‘, ‘) AS category FROM member_directory md LEFT JOIN member_categories mc ON md.id = mc.member_id LEFT JOIN categories ON mc.category_id = categories.id WHERE mc.category_id = 187 GROUP BY md.id ORDER BY md.id ASC, md.name ASC LIMIT 0, 10

====================================================================
id | category |
——————————————————————–
1417 | SHOPPING |
1736 | SHOPPING |
1768 | SHOPPING |
2219 | SHOPPING |
2403 | SHOPPING |
2407 | SHOPPING |
2426 | SHOPPING |
2431 | SHOPPING |
2456 | SHOPPING |
2458 | SHOPPING |
====================================================================

Is there any way I can get the desired result? I just need a query to get information from the member_directory and any categories it may belong to.

mysql> SELECT * FROM user where FIND_IN_SET(id, @lid);
+—-+———-+
| id | nom |
+—-+———-+
| 4 | julie |
| 6 | renaud |
| 9 | aurelien |
+—-+———-+
3 rows in set (0.02 sec)

I’ve a little problem using group_concat and user variable.
I tried to set a group_concat(id) result into a @var, and then call the same table where id in(@var)
but mysql return only the first row :\ do u have any idea ?

Here is the code :
——————
CREATE TABLE IF NOT EXISTS `user` (
`id` tinyint(3) unsigned NOT NULL AUTO_INCREMENT,
`nom` varchar(255) NOT NULL,
PRIMARY KEY (`id`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8 AUTO_INCREMENT=10 ;
INSERT INTO `user` (`id`, `nom`) VALUES (1, ‘flo’),(2, ’seb’),(3, ‘julien’),(4, ‘julie’),(5, ‘aymeric’),(6, ‘renaud’),(7, ‘lucy’),(8, ‘charlotte’),(9, ‘aurelien’);

mysql> SELECT @lid := CAST(GROUP_CONCAT(id) AS CHAR) FROM `user` WHERE `nom` in(’renaud’, ‘julie’, ‘lucy’);
+—————————————-+
| @lid := CAST(GROUP_CONCAT(id) AS CHAR) |
+—————————————-+
| 4,6,7 |
+—————————————-+
1 row in set (0.00 sec)

mysql> SELECT @lid;
+——-+
| @lid |
+——-+
| 4,6,7 |
+——-+
1 row in set (0.00 sec)

mysql> SELECT * FROM user WHERE id IN(@lid);
+—-+——-+
| id | nom |
+—-+——-+
| 4 | julie |
+—-+——-+
1 row in set (0.00 sec)

I know it is totally useless but it’s just a sample

Regards.