MDEV-5103: server crashed on singular Item_equal

Singular Item_equal support added.

The problem was that during constant table substitution Item_equal become containing only one constant which was not supported internally.

2 files changed, 22 insertions, 1 deletions

diff --git a/sql/item_cmpfunc.cc b/sql/item_cmpfunc.cc
index d1075c3c47f..22554c71d90 100644
--- a/sql/item_cmpfunc.cc
+++ b/sql/item_cmpfunc.cc
@@ -5564,6 +5564,12 @@ void Item_equal::add_const(Item *c, Item *f)
     func->quick_fix_field();
     cond_false= !func->val_int();
   }
+  /*
+    TODO: also support the case where Item_equal becomes singular with
+    this->is_cond_true()=1.  When I attempted to mark the item as constant,
+    the optimizer attempted to remove it, however it is still referenced from
+    COND_EQUAL and I got a crash.
+  */
   if (cond_false)
     const_item_cache= 1;
 }
@@ -5768,7 +5774,8 @@ void Item_equal::merge_into_list(List<Item_equal> *list,
 
 void Item_equal::sort(Item_field_cmpfunc compare, void *arg)
 {
-  bubble_sort<Item>(&equal_items, compare, arg);
+  if (equal_items.elements > 1)
+    bubble_sort<Item>(&equal_items, compare, arg);
 }
 
 
@@ -5868,6 +5875,12 @@ bool Item_equal::fix_fields(THD *thd, Item **ref)
 void Item_equal::update_used_tables()
 {
   not_null_tables_cache= used_tables_cache= 0;
+  /*
+    TODO: also support the case where Item_equal becomes singular with
+    this->is_cond_true()=1.  When I attempted to mark the item as constant,
+    the optimizer attempted to remove it, however it is still referenced from
+    COND_EQUAL and I got a crash.
+  */
   if ((const_item_cache= cond_false))
     return;
   Item_equal_fields_iterator it(*this);
@@ -5916,6 +5929,8 @@ longlong Item_equal::val_int()
 {
   if (cond_false)
     return 0;
+  if (is_cond_true())
+    return 1;
   Item *item= get_const();
   Item_equal_fields_iterator it(*this);
   if (!item)
@@ -5940,6 +5955,11 @@ longlong Item_equal::val_int()
 void Item_equal::fix_length_and_dec()
 {
   Item *item= get_first(NO_PARTICULAR_TAB, NULL);
+  if (!item)
+  {
+    DBUG_ASSERT(is_cond_true()); // it should be the only constant
+    item= equal_items.head();
+  }
   eval_item= cmp_item::get_comparator(item->cmp_type(), item,
                                       item->collation.collation);
 }
diff --git a/sql/item_cmpfunc.h b/sql/item_cmpfunc.h
index c1ef680f3ee..cdb4963e857 100644
--- a/sql/item_cmpfunc.h
+++ b/sql/item_cmpfunc.h
@@ -1725,6 +1725,7 @@ public:
   Item_equal(Item_equal *item_equal);
   /* Currently the const item is always the first in the list of equal items */
   inline Item* get_const() { return with_const ? equal_items.head() : NULL; }
+  inline bool is_cond_true() { return equal_items.elements == 1; }
   void add_const(Item *c, Item *f = NULL);
   /** Add a non-constant item to the multiple equality */
   void add(Item *f) { equal_items.push_back(f); }