I tried to upgrade Moodle 2.2.1 to 2.6.2+ and got this error message:
Default exception handler: DDL sql execution error Debug: Data truncated for column 'institution' at row 999 ALTER TABLE mdl_user MODIFY COLUMN institution VARCHAR(255) CHARACTER SET utf8 COLLATE utf8_general_ci NOT NULL DEFAULT '' after phone2 Error code: ddlexecuteerror
The solution was to run these sql’s at the Mysql database:
update mdl_user set institution="" where institution is NULL; update mdl_user set department="" where department is NULL; update mdl_user set address="" where address is NULL;
This issue seems to be related to: