MySQL and GROUP_CONCAT() maximum length - mysql

Question

I'm using GROUP_CONCAT() in a MySQL query to convert multiple rows into a single string.
However, the maximum length of the result of this function is 1024 characters.
I'm very well aware that I can change the param group_concat_max_len to increase this limit:
SET SESSION group_concat_max_len = 1000000;
However, on the server I'm using, I can't change any param. Not by using the preceding query and not by editing any configuration file.
So my question is:
Is there any other way to get the output of a multiple row query into a single string?

Answer 1

SET SESSION group_concat_max_len = 1000000;
is a temporary, session-scope, setting. It only applies to the current session You should use it like this.
SET SESSION group_concat_max_len = 1000000;
select group_concat(column) from table group by column
You can do this even in sharing hosting, but when you use an other session, you need to repeat the SET SESSION command.

Answer 2

The correct parameter to set the maximum length is:
SET ##group_concat_max_len = value_numeric;
value_numeric must be > 1024; by default the group_concat_max_len value is 1024.

Answer 3

Include this setting in xampp my.ini configuration file:
[mysqld]
group_concat_max_len = 1000000
Then restart xampp mysql

Answer 4

You can try this
SET GLOBAL group_concat_max_len = 1000000;

Answer 5

The correct syntax is mysql> SET ##global.group_concat_max_len = integer;
If you do not have the privileges to do this on the server where your database resides then use a query like:
mySQL="SET ##session.group_concat_max_len = 10000;"or a different value. Next line:
SET objRS = objConn.Execute(mySQL) your variables may be different.
then
mySQL="SELECT GROUP_CONCAT(......);" etc
I use the last version since I do not have the privileges to change the default value of 1024 globally (using cPanel).
Hope this helps.

Answer 6

The short answer: the setting needs to be setup when the connection to the MySQL server is established. For example, if using MYSQLi / PHP, it will look something like this:
$ myConn = mysqli_init();
$ myConn->options(MYSQLI_INIT_COMMAND, 'SET SESSION group_concat_max_len = 1000000');
Therefore, if you are using a home-brewed framework, well, you need to look for the place in the code when the connection is establish and provide a sensible value.
I am still using Codeigniter 3 on 2020, so in this framework, the code to add is in the application/system/database/drivers/mysqli/mysqli_driver.php, the function is named db_connect();
public function db_connect($persistent = FALSE)
{
// Do we have a socket path?
if ($this->hostname[0] === '/')
{
$hostname = NULL;
$port = NULL;
$socket = $this->hostname;
}
else
{
$hostname = ($persistent === TRUE)
? 'p:'.$this->hostname : $this->hostname;
$port = empty($this->port) ? NULL : $this->port;
$socket = NULL;
}
$client_flags = ($this->compress === TRUE) ? MYSQLI_CLIENT_COMPRESS : 0;
$this->_mysqli = mysqli_init();
$this->_mysqli->options(MYSQLI_OPT_CONNECT_TIMEOUT, 10);
$this->_mysqli->options(MYSQLI_INIT_COMMAND, 'SET SESSION group_concat_max_len = 1000000');
...
}

Answer 7

CREATE TABLE some_table (
field1 int(11) NOT NULL AUTO_INCREMENT,
field2 varchar(10) NOT NULL,
field3 varchar(10) NOT NULL,
PRIMARY KEY (`field1`)
);
INSERT INTO `some_table` (field1, field2, field3) VALUES
(1, 'text one', 'foo'),
(2, 'text two', 'bar'),
(3, 'text three', 'data'),
(4, 'text four', 'magic');
This query is a bit strange but it does not need another query to initialize the variable; and it can be embedded in a more complex query.
It returns all the 'field2's separated by a semicolon.
SELECT result
FROM (SELECT #result := '',
(SELECT result
FROM (SELECT #result := CONCAT_WS(';', #result, field2) AS result,
LENGTH(#result) AS blength
FROM some_table
ORDER BY blength DESC
LIMIT 1) AS sub1) AS result) AS sub2;