Bug#35981: ALTER EVENT causes the server to change the PRESERVE option.

If [NOT] PRESERVE was not given, parser always defaulted to NOT
PRESERVE, making it impossible for the "not given = no change"
rule to work in ALTER EVENT. Leaving out the PRESERVE-clause
defaults to NOT PRESERVE on CREATE now, and to "no change" in
ALTER.

mysql-test/r/events_2.result:
  show that giving no PRESERVE-clause to ALTER EVENT
  results in no change. show that giving no PRESERVE-clause
  to CREATE EVENT defaults to NOT PRESERVE as per the docs.
  Show specifically that this is also handled correctly when
  trying to ALTER EVENTs into the past.
mysql-test/t/events_2.test:
  show that giving no PRESERVE-clause to ALTER EVENT
  results in no change. show that giving no PRESERVE-clause
  to CREATE EVENT defaults to NOT PRESERVE as per the docs.
  Show specifically that this is also handled correctly when
  trying to ALTER EVENTs into the past.
sql/event_db_repository.cc:
  If ALTER EVENT was given no PRESERVE-clause (meaning "no change"),
  we don't know the previous PRESERVE-setting by the time we check
  the parse-data. If ALTER EVENT was given dates that are in the past,
  we don't know how to react, lacking the PRESERVE-setting. Heal this
  by running the check later when we have actually read the previous
  EVENT-data.
sql/event_parse_data.cc:
  Change default for ON COMPLETION to indicate, "not specified."
  Also defer throwing errors when ALTER EVENT is given dates in
  the past but not PRESERVE-clause until we know the previous
  PRESERVE-value.
sql/event_parse_data.h:
  Add third state for ON COMPLETION [NOT] PRESERVE (preserve,
  don't, not specified).
  
  Make check_dates() public so we can defer this check until
  deeper in the callstack where we have all the required data.
sql/sql_yacc.yy:
  If CREATE EVENT is not given ON COMPLETION [NOT] PRESERVE,
  we default to NOT, as per the docs.

1 files changed, 14 insertions, 0 deletions

diff --git a/sql/event_db_repository.cc b/sql/event_db_repository.cc
index 401f76f5d26..e33cae18cee 100644
--- a/sql/event_db_repository.cc
+++ b/sql/event_db_repository.cc
@@ -185,6 +185,8 @@ mysql_event_fill_row(THD *thd,
   DBUG_PRINT("info", ("dbname=[%s]", et->dbname.str));
   DBUG_PRINT("info", ("name  =[%s]", et->name.str));
 
+  DBUG_ASSERT(et->on_completion != Event_parse_data::ON_COMPLETION_DEFAULT);
+
   if (table->s->fields < ET_FIELD_COUNT)
   {
     /*
@@ -745,6 +747,18 @@ Event_db_repository::update_event(THD *thd, Event_parse_data *parse_data,
 
   store_record(table,record[1]);
 
+  /*
+    We check whether ALTER EVENT was given dates that are in the past.
+    However to know how to react, we need the ON COMPLETION type. The
+    check is deferred to this point because by now we have the previous
+    setting (from the event-table) to fall back on if nothing was specified
+    in the ALTER EVENT-statement.
+  */
+
+  if (parse_data->check_dates(thd,
+                              table->field[ET_FIELD_ON_COMPLETION]->val_int()))
+    goto end;
+
   /* Don't update create on row update. */
   table->timestamp_field_type= TIMESTAMP_NO_AUTO_SET;