Mysql same DB, same query, different users – different error messages

On the face of it, that does seem impossible.

The thing is, your error suggests it's not that you're trying to delete at all.

The message you're getting suggests you're trying to insert or update a row in the child table, not delete a row from the parent table. If the foreign key you posted was causing the problem relative to a delete, you should see this message, instead:

Cannot delete or update a parent row: a foreign key constraint fails (`test`.`bar`, CONSTRAINT `bar_ibfk_1` FOREIGN KEY (`foo_id`) REFERENCES `foo` (`id`))

It's also possible you have some BEFORE DELETE trigger magic on survey_main that's doing something unexpected.

Right after this error occurs, try this:

SHOW ENGINE INNODB STATUS;

The LATEST FOREIGN KEY ERROR section should give you something more to go on. Failing that, you could enable the general log, which will show queries executed by triggers and other stored programs, as well as the queries you're directly executing, to shed light on what might be going on behind the scenes.

Update (#1) Things are definitely not as they seem and the full table definitions are going to be pretty critical, here.

Also, the version of MySQL you're using may also be relevant, so please mention it.

With nothing more to go on at the moment, I'm speculating that you have invalid data in the survey_id column of the survey_answers table. To test that theory:

SELECT *
  FROM survey_answers sa
  LEFT JOIN survey_main sm ON sm.id = sa.survey_id
 WHERE sm.id IS NULL;

If I understand your schema correctly, then this query will return zero rows if I am wrong. :) If you get rows returned, then those rows have survey_answers records that contain an survey_id value that doesn't exist in the id column of survey_main.

You need to disable foreign key checks and unique checks

#!/bin/bash
DATABASES=$(mysql -u XXXXX -pXXXXX --skip-column-names -e 'select distinct(table_schema) from information_schema.tables where table_schema not in ("mysql","information_schema","performance_schema")')
for D in $DATABASES
do
   TABLES=$(mysql -u XXXXX -pXXXXX --skip-column-names -e 'select table_name from information_schema.tables where table_schema="'$D'" and engine="InnoDB"')
   for T in $TABLES
   do
      echo "ALTERING TABLE $T"
      SQL="SET FOREIGN_KEY_CHECKS = 0; SET UNIQUE_CHECKS = 0;"
      SQL="${SQL} ALTER TABLE ${T} ENGINE=MYISAM"
      mysql -u XXXXX -pXXXXX -D${D} -e "${SQL}"
   done
done

Here is a more concise way: Reload data with InnoDB Disabled

#!/bin/bash
DATABASES=$(mysql -u XXXXX -pXXXXX --skip-column-names -e 'select distinct(table_schema) from information_schema.tables where table_schema not in ("mysql","information_schema","performance_schema")')
mysqldump -u XXXXX -pXXXXX --single-transaction --add-drop-database -B ${DATABASES} > AllMyData.sql
mysql -u XXXXX -pXXXXX -e"SET GLOBAL innodb_fast_shutdown = 0"
service mysql restart --skip-innodb
mysql -u XXXXX -pXXXXX < AllMyData.sql