MDEV-9604 crash in Item::save_in_field with empty enum value

1. Fixing Field_time::get_equal_const_item() to pass TIME_FUZZY_DATES
   and TIME_INVALID_DATES to get_time_with_conversion().
   This is needed to make the recursively called Item::get_date() return
   non-NULL values on garbage input. This makes Field_time::get_equal_const_item()
   work consistently with how Item::val_time_packed() works.

2. Fixing Item::get_date() to return TIME'00:00:00' rather than
   DATE'0000-00-00' on empty or garbage input when:
   - TIME_FUZZY_DATES is enabled
   - The caller requested a TIME value (by passing TIME_TIME_ONLY).
   This is needed to avoid conversion of DATE'0000-00-00' to TIME
   in get_time_with_conversion(), which would erroneously try to subtract
   CURRENT_DATE from DATE'0000-00-00' and return TIME'-838:59:59' rather than
   the desired zero value TIME'00:00:00'.

   #1 and #2 fix these type of scripts to return one row with both
   MyISAM and InnoDB, with and without an index on t1.b:

     CREATE TABLE t1 (a ENUM('a'), b TIME, c INT, KEY(b));
     INSERT INTO t1 VALUES ('','00:00:00',0);
     SELECT * FROM t1 WHERE b='';
     SELECT * FROM t1 WHERE a=b;
     SELECT * FROM t1 IGNORE INDEX(b) WHERE b='';
     SELECT * FROM t1 IGNORE INDEX(b) WHERE a=b;

   Additionally, #1 and #2 fix the originally reported in MDEV-9604 crash
   in Item::save_in_field(), because now execution goes through a different
   path, so save_in_field() is called for a Item_time_literal instance
   (which is non-NULL) rather than a Item_cache_str instance (which could
   return NULL without setting null_value).

3. Fixing Field_temporal::get_equal_const_item_datetime() to enable
   equal field propagation for DATETIME and TIMESTAMP in case of
   comparison (e.g. when ANY_SUBST), for symmetry with
   Field_newdate::get_equal_const_item(). This fixes a number of problems
   with empty set returned on comparison to empty/garbage input.
   Now all SELECT queries in this script return one row for MyISAM and InnoDB,
   with and without an index on t1.b:

     CREATE TABLE t1 (a ENUM('a'), b DATETIME, c INT, KEY(b));
     INSERT INTO t1 VALUES ('','0000-00-00 00:00:00',0);
     SELECT * FROM t1 WHERE b='';
     SELECT * FROM t1 WHERE a=b;
     SELECT * FROM t1 IGNORE INDEX(b) WHERE b='';
     SELECT * FROM t1 IGNORE INDEX(b) WHERE a=b;

1 files changed, 16 insertions, 1 deletions

diff --git a/sql/field.cc b/sql/field.cc
index 895f8a00f10..ffa7beb275b 100644
--- a/sql/field.cc
+++ b/sql/field.cc
@@ -5624,6 +5624,18 @@ Item *Field_temporal::get_equal_const_item_datetime(THD *thd,
     }
     break;
   case ANY_SUBST:
+    if (!is_temporal_type_with_date(const_item->field_type()))
+    {
+      MYSQL_TIME ltime;
+      if (const_item->get_date_with_conversion(&ltime,
+                                               TIME_FUZZY_DATES |
+                                               TIME_INVALID_DATES))
+        return NULL;
+      return new (thd->mem_root)
+        Item_datetime_literal_for_invalid_dates(thd, &ltime,
+                                                ltime.second_part ?
+                                                TIME_SECOND_PART_DIGITS : 0);
+    }
     break;
   }
   return const_item;
@@ -5932,7 +5944,10 @@ Item *Field_time::get_equal_const_item(THD *thd, const Context &ctx,
     {
       MYSQL_TIME ltime;
       // Get the value of const_item with conversion from DATETIME to TIME
-      if (const_item->get_time_with_conversion(thd, &ltime, TIME_TIME_ONLY))
+      if (const_item->get_time_with_conversion(thd, &ltime,
+                                               TIME_TIME_ONLY |
+                                               TIME_FUZZY_DATES |
+                                               TIME_INVALID_DATES))
         return NULL;
       /*
         Replace a DATE/DATETIME constant to a TIME constant: