If you get this error with MediaWiki (or any other software) you should look at the properties of your table structure. Most probable is that an “auto_increment” is missing. This problem took me quite a while to find, especially because of lots of people on the web come up with the weirdest explanations and solutions, like simply reinstalling and re-importing the data. Not fun if you are in a hurry and have a table with 7.5 million text files.

This is one of those ‘OMG Eriky, you saved my ass!’ posts.

You probably came here after searching for this error. Before you try anything else, check if your /tmp directory exists and if it has the right permissions. If not, create it and do a “chmod 777 /tmp”. MySQL will give you the weirdest errors if it can not use the /tmp folder.

If this does not help, check your /etc/mysql/my.cnf. There could be a line somewhere, stating which directory to use as a temporary directory. Create that directory, or remove/change the line so MySQL uses your /tmp folder instead.