Reported by one of our clients:

When I try to delete a question in a questionnaire that I am editing, I get the message:
Error reading from database

More information about this error
Debug info: ERROR: operator does not exist: character varying = integer
LINE 1: ..._table FROM mdl_questionnaire_question_type WHERE typeid = 1
^
HINT: No operator matches the given name and argument type(s). You might need to add explicit type casts.
SELECT response_table FROM mdl_questionnaire_question_type WHERE typeid = 1
[array (
)]
Error code: dmlreadexception
Stack trace:

line 443 of /lib/dml/moodle_database.php: dml_read_exception thrown
line 244 of /lib/dml/pgsql_native_moodle_database.php: call to moodle_database->query_end()
line 764 of /lib/dml/pgsql_native_moodle_database.php: call to pgsql_native_moodle_database->query_end()
line 1478 of /lib/dml/moodle_database.php: call to pgsql_native_moodle_database->get_records_sql()
line 599 of /mod/questionnaire/questions.php: call to moodle_database->get_record_sql()