MDEV-6855 Assertion `cond_type == Item::FUNC_ITEM' failed in check_group_min_max_predicates with GROUP BY, aggregate in WHERE SQ, multi-part key

mysql-test/r/group_by.result:
  Test for MDEV-6855
mysql-test/t/group_by.test:
  Test for MDEV-6855
sql/item.h:
  Fixed spelling error
sql/opt_range.cc:
  Added handling of cond_type == Item::CACHE_ITEM in WHERE clauses for MIN/MAX optimization.
  Fixed indentation

mysql-test/r/group_by.result

@@ -2493,3 +2493,17 @@ SELECT i2 FROM t1 AS t1a STRAIGHT_JOIN ( t2 INNER JOIN t1 AS t1b ON (t1b.c1 = c2
 WHERE t1a.c1 = c2 GROUP BY i2;
 i2
 DROP TABLE t1,t2;
+#
+# MDEV-6855
+# MIN(*) with subqueries with IS NOT NULL in WHERE clause crashed.
+#
+CREATE TABLE t1 (i INT, c VARCHAR(3), KEY(c,i)) ENGINE=MyISAM;
+INSERT INTO t1 VALUES (7,'foo'),(0,'bar');
+CREATE TABLE t2 (j INT) ENGINE=MyISAM;
+INSERT INTO t2 VALUES (0),(8),(1),(8),(9);
+SELECT MAX(i), c FROM t1 
+WHERE c != 'qux' AND ( SELECT SUM(j) FROM t1, t2 ) IS NOT NULL GROUP BY c;
+MAX(i)	c
+0	bar
+7	foo
+drop table t1,t2;

mysql-test/t/group_by.test

@@ -1665,6 +1665,21 @@ WHERE t1a.c1 = c2 GROUP BY i2;
 
 DROP TABLE t1,t2;
 
+--echo #
+--echo # MDEV-6855
+--echo # MIN(*) with subqueries with IS NOT NULL in WHERE clause crashed.
+--echo #
+
+CREATE TABLE t1 (i INT, c VARCHAR(3), KEY(c,i)) ENGINE=MyISAM;
+INSERT INTO t1 VALUES (7,'foo'),(0,'bar');
+
+CREATE TABLE t2 (j INT) ENGINE=MyISAM;
+INSERT INTO t2 VALUES (0),(8),(1),(8),(9);
+
+SELECT MAX(i), c FROM t1 
+WHERE c != 'qux' AND ( SELECT SUM(j) FROM t1, t2 ) IS NOT NULL GROUP BY c;
+drop table t1,t2;
+
 #
 # End of MariaDB 5.5 tests
 #

sql/item.h

@@ -4038,7 +4038,7 @@ private:
 /**
   @todo
   Implement the is_null() method for this class. Currently calling is_null()
-  on any Item_cache object resolves to Item::is_null(), which reutns FALSE
+  on any Item_cache object resolves to Item::is_null(), which returns FALSE
   for any value.
 */
 

sql/opt_range.cc

@@ -12539,12 +12539,13 @@ get_best_group_min_max(PARAM *param, SEL_TREE *tree, double read_time)
 
   SYNOPSIS
     check_group_min_max_predicates()
-    cond        [in]  the expression tree being analyzed
+    cond            [in]  the expression tree being analyzed
-    min_max_arg [in]  the field referenced by the MIN/MAX function(s)
+    min_max_arg     [in]  the field referenced by the MIN/MAX function(s)
-    image_type  [in]
+    image_type      [in]
-    has_min_max_arg [out] true if the subtree being analyzed references min_max_arg
+    has_min_max_arg [out] true if the subtree being analyzed references
-    has_other_arg   [out] true if the subtree being analyzed references a column
+                          min_max_arg
-                          other min_max_arg
+    has_other_arg   [out] true if the subtree being analyzed references a
+                          column other min_max_arg
 
   DESCRIPTION
     The function walks recursively over the cond tree representing a WHERE
@@ -12588,7 +12589,7 @@ check_group_min_max_predicates(Item *cond, Item_field *min_max_arg_item,
         (2) the subtree passes the test, but it is an OR and it references both
             the min/max argument and other columns.
       */
-      if (!check_group_min_max_predicates(and_or_arg, min_max_arg_item,      //1
+      if (!check_group_min_max_predicates(and_or_arg, min_max_arg_item,     //1
                                           image_type,
                                           &has_min_max, &has_other) ||
           (func_type == Item_func::COND_OR_FUNC && has_min_max && has_other))//2
@@ -12604,7 +12605,7 @@ check_group_min_max_predicates(Item *cond, Item_field *min_max_arg_item,
     a subquery in the WHERE clause.
   */
 
-  if (cond_type == Item::SUBSELECT_ITEM)
+  if (unlikely(cond_type == Item::SUBSELECT_ITEM))
   {
     Item_subselect *subs_cond= (Item_subselect*) cond;
     if (subs_cond->is_correlated)
@@ -12621,7 +12622,14 @@ check_group_min_max_predicates(Item *cond, Item_field *min_max_arg_item,
     }
     DBUG_RETURN(TRUE);
   }
-
+  /*
+    Subquery with IS [NOT] NULL
+    TODO: Look into the cache_item and optimize it like we do for
+    subselect's above
+   */
+  if (unlikely(cond_type == Item::CACHE_ITEM))
+    DBUG_RETURN(cond->const_item());
+  
   /*
     Condition of the form 'field' is equivalent to 'field <> 0' and thus
     satisfies the SA3 condition.
@@ -12638,7 +12646,9 @@ check_group_min_max_predicates(Item *cond, Item_field *min_max_arg_item,
 
   /* We presume that at this point there are no other Items than functions. */
   DBUG_ASSERT(cond_type == Item::FUNC_ITEM);
-
+  if (unlikely(cond_type != Item::FUNC_ITEM))   /* Safety */
+    DBUG_RETURN(FALSE);
+  
   /* Test if cond references only group-by or non-group fields. */
   Item_func *pred= (Item_func*) cond;
   Item_func::Functype pred_type= pred->functype();