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, 43 insertions, 1 deletions

diff --git a/sql/event_parse_data.cc b/sql/event_parse_data.cc
index e87e4593f8f..df419e92d0d 100644
--- a/sql/event_parse_data.cc
+++ b/sql/event_parse_data.cc
@@ -45,7 +45,7 @@ Event_parse_data::new_instance(THD *thd)
 */
 
 Event_parse_data::Event_parse_data()
-  :on_completion(Event_parse_data::ON_COMPLETION_DROP),
+  :on_completion(Event_parse_data::ON_COMPLETION_DEFAULT),
   status(Event_parse_data::ENABLED),
   do_not_create(FALSE),
   body_changed(FALSE),
@@ -114,6 +114,12 @@ Event_parse_data::check_if_in_the_past(THD *thd, my_time_t ltime_utc)
   if (ltime_utc >= (my_time_t) thd->query_start())
     return;
 
+  /*
+    We'll come back later when we have the real on_completion value
+  */
+  if (on_completion == Event_parse_data::ON_COMPLETION_DEFAULT)
+    return;
+
   if (on_completion == Event_parse_data::ON_COMPLETION_DROP)
   {
     switch (thd->lex->sql_command) {
@@ -142,6 +148,42 @@ Event_parse_data::check_if_in_the_past(THD *thd, my_time_t ltime_utc)
 
 
 /*
+  Check time/dates in ALTER EVENT
+
+  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. Hence,
+  the check is deferred until we have the previous ON COMPLETION type
+  from the event-db to fall back on if nothing was specified in the
+  ALTER EVENT-statement.
+
+  SYNOPSIS
+    Event_parse_data::check_dates()
+      thd            Thread
+      on_completion  ON COMPLETION value currently in event-db.
+                     Will be overridden by value in ALTER EVENT if given.
+
+  RETURN VALUE
+    TRUE            an error occurred, do not ALTER
+    FALSE           OK
+*/
+
+bool
+Event_parse_data::check_dates(THD *thd, int previous_on_completion)
+{
+  if (on_completion == Event_parse_data::ON_COMPLETION_DEFAULT)
+  {
+    on_completion= previous_on_completion;
+    if (!ends_null)
+      check_if_in_the_past(thd, ends);
+    if (!execute_at_null)
+      check_if_in_the_past(thd, execute_at);
+  }
+  return do_not_create;
+}
+
+
+
+/*
   Sets time for execution for one-time event.
 
   SYNOPSIS