MySQL GROUP_CONCAT returns [BLOB – 14 B]

A tech post today, I really don’t do enough of these. I bumped into an issue recently where I was building a form guide for the cricket league website that I run. The idea was to present the team form on one line based off results in my scorecard table, like so: WWWLLWWNWWLWW

I previously had a nice little PHP script which handled Wins versus Losses quite well but I needed to add Tie, Draw and No Result to the mix. I had a bit of a play with PHP but decided to have a crack in MySQL instead.

Which works great but the ordering wasn’t as I wanted, for a proper form guide it needs to be in order of games played. Hence I added the ORDER BY:

The problem is that in my environment the value being returned for the Form field was [BLOB – 14 B]. It turns out the result value depends on the system variable group_concat_max_len. The default values for this is 1024 (1kb) and mine was obviously coming out larger. I verified my group_concat_max_len was set to 1024 with the following query:

If you want to change the the length of that system variable use can use the below query:

If you have access to my.ini or my.cnf you can also do the following:

  • Open your my.ini or my.cnf file;
  • Change the value of the group_concat_max_len system variable to 512 (no ‘k’ suffix);
  • Restart the mysql service

I also found a solution that works, and is working well for me. I converted the group concat to utf8 with the following sql:

Hopefully helps someone else having the same issue.

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Australian. Sport. Passionate Cricket Fan. Go Pro. Abseiling. Snorkeling. Travel. Golf R. SQL Server Developer. Three sons. One daughter. Last Trip: Tasmania.


    • Troy R
    • May 27, 2010
    • Reply

    Keep up your tech posts, enjoy the read 🙂

  1. Haha, cheers Troy! This is probably all piddly stuff to you though!

    • mansih
    • January 24, 2011
    • Reply

    Hello MIke,

    Its usfully page, but can you explain why required CONVERT in UTF 8.

  2. My understanding is because my BLOB is stored as UTF 8.

    • Chintan Patel
    • December 9, 2012
    • Reply

    Thank’s For this Solution…
    I have tryed google but fail….

  3. Thanks for the CONVERT tip, helped me out!

  4. Very glad folks!

    • Guillermo Malagón
    • March 27, 2014
    • Reply

    Hey man, NICE!
    this works if you dont receive special chars, but what happens if i use “ñ, à,á”
    if you convert to utf8 the words get cut when they find those chars, what else can we use????

    • Guillermo Malagón
    • March 27, 2014
    • Reply

    ok got it!!!! (latin1)

    SPANISH : USING latin1

    • Nice Guillermo, thanks for your input!

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