MySQL and GROUP_CONCAT() maximum length

问题

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?

回答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.

回答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.

回答3:

Include this setting in xampp my.ini configuration file:

[mysqld]
group_concat_max_len = 1000000

Then restart xampp mysql

回答4:

You can try this

SET GLOBAL group_concat_max_len = 1000000;

回答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.

回答6:

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;

来源：https://stackoverflow.com/questions/2567000/mysql-and-group-concat-maximum-length

标签

mysql

group-concat