MDEV-29294 Assertion `functype() == ((Item_cond *) new_item)->functype()'...

MDEV-29294 Assertion `functype() == ((Item_cond *) new_item)->functype()' failed in Item_cond::remove_eq_conds on SELECT

Item_singlerow_subselect may be converted to Item_cond during
optimization. So there is a possibility of constructing nested
Item_cond_and or Item_cond_or which is not allowed (such
conditions must be flattened).
This commit checks if such kind of optimization has been applied
and flattens the condition if needed

mysql-test/main/select.result

@@ -5639,4 +5639,60 @@ EXECUTE stmt;
 COUNT(DISTINCT a)
 3
 DROP TABLE t1;
+#
+# MDEV-29294: Assertion `functype() == ((Item_cond *) new_item)->functype()'
+#             failed in Item_cond::remove_eq_conds on SELECT
+#
+CREATE TABLE t1 (a INT);
+INSERT INTO t1 VALUES (1),(2),(3);
+# Test for nested OR conditions:
+SELECT * FROM t1 WHERE a = 1 AND
+(3 = 0 OR (SELECT a = 1 OR (SELECT 3 WHERE a = a) = 3));
+a
+1
+EXPLAIN EXTENDED
+SELECT * FROM t1 WHERE a = 1 AND
+(3 = 0 OR (SELECT a = 1 OR (SELECT 3 WHERE a = a) = 3));
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	3	100.00	Using where; Using temporary
+3	DEPENDENT SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
+Warnings:
+Note	1276	Field or reference 'test.t1.a' of SELECT #2 was resolved in SELECT #1
+Note	1276	Field or reference 'test.t1.a' of SELECT #3 was resolved in SELECT #1
+Note	1276	Field or reference 'test.t1.a' of SELECT #3 was resolved in SELECT #1
+Note	1249	Select 2 was reduced during optimization
+Note	1003	/* select#1 */ select `test`.`t1`.`a` AS `a` from `test`.`t1` where `test`.`t1`.`a` = 1 and (1 or <expr_cache><`test`.`t1`.`a`>((/* select#3 */ select 3 from DUAL  where `test`.`t1`.`a` = `test`.`t1`.`a`)) = 3)
+PREPARE stmt FROM 'SELECT * FROM t1 WHERE a = 1 AND
+  (3 = 0 OR (SELECT a = 1 OR (SELECT 3 WHERE a = a) = 3))';
+EXECUTE stmt;
+a
+1
+EXECUTE stmt;
+a
+1
+CREATE VIEW v1 AS SELECT * FROM t1 WHERE a = 1 AND
+(3 = 0 OR (SELECT a = 1 OR (SELECT 3 WHERE a = a) = 3));
+SELECT * FROM v1;
+a
+1
+# Test for nested AND conditions:
+SELECT * FROM t1 WHERE a = 1 OR
+(3 = 3 AND (SELECT a = 1 AND (SELECT 3 WHERE a = a) = 3));
+a
+1
+PREPARE stmt FROM 'SELECT * FROM t1 WHERE a = 1 OR
+  (3 = 3 AND (SELECT a = 1 AND (SELECT 3 WHERE a = a) = 3))';
+EXECUTE stmt;
+a
+1
+EXECUTE stmt;
+a
+1
+CREATE VIEW v2 AS SELECT * FROM t1 WHERE a = 1 OR
+(3 = 3 AND (SELECT a = 1 AND (SELECT 3 WHERE a = a) = 3));
+SELECT * FROM v2;
+a
+1
+DROP TABLE t1;
+DROP VIEW v1, v2;
 End of 10.0 tests

mysql-test/main/select.test

@@ -4742,4 +4742,44 @@ EXECUTE stmt;
 --enable_warnings
 DROP TABLE t1;
 
+--echo #
+--echo # MDEV-29294: Assertion `functype() == ((Item_cond *) new_item)->functype()'
+--echo #             failed in Item_cond::remove_eq_conds on SELECT
+--echo #
+CREATE TABLE t1 (a INT);
+INSERT INTO t1 VALUES (1),(2),(3);
+
+--echo # Test for nested OR conditions:
+SELECT * FROM t1 WHERE a = 1 AND
+  (3 = 0 OR (SELECT a = 1 OR (SELECT 3 WHERE a = a) = 3));
+
+EXPLAIN EXTENDED
+SELECT * FROM t1 WHERE a = 1 AND
+  (3 = 0 OR (SELECT a = 1 OR (SELECT 3 WHERE a = a) = 3));
+
+PREPARE stmt FROM 'SELECT * FROM t1 WHERE a = 1 AND
+  (3 = 0 OR (SELECT a = 1 OR (SELECT 3 WHERE a = a) = 3))';
+EXECUTE stmt;
+EXECUTE stmt;
+
+CREATE VIEW v1 AS SELECT * FROM t1 WHERE a = 1 AND
+  (3 = 0 OR (SELECT a = 1 OR (SELECT 3 WHERE a = a) = 3));
+SELECT * FROM v1;
+
+--echo # Test for nested AND conditions:
+SELECT * FROM t1 WHERE a = 1 OR
+  (3 = 3 AND (SELECT a = 1 AND (SELECT 3 WHERE a = a) = 3));
+
+PREPARE stmt FROM 'SELECT * FROM t1 WHERE a = 1 OR
+  (3 = 3 AND (SELECT a = 1 AND (SELECT 3 WHERE a = a) = 3))';
+EXECUTE stmt;
+EXECUTE stmt;
+
+CREATE VIEW v2 AS SELECT * FROM t1 WHERE a = 1 OR
+  (3 = 3 AND (SELECT a = 1 AND (SELECT 3 WHERE a = a) = 3));
+SELECT * FROM v2;
+
+DROP TABLE t1;
+DROP VIEW v1, v2;
+
 --echo End of 10.0 tests

mysql-test/main/select_jcl6.result

@@ -5650,6 +5650,62 @@ EXECUTE stmt;
 COUNT(DISTINCT a)
 3
 DROP TABLE t1;
+#
+# MDEV-29294: Assertion `functype() == ((Item_cond *) new_item)->functype()'
+#             failed in Item_cond::remove_eq_conds on SELECT
+#
+CREATE TABLE t1 (a INT);
+INSERT INTO t1 VALUES (1),(2),(3);
+# Test for nested OR conditions:
+SELECT * FROM t1 WHERE a = 1 AND
+(3 = 0 OR (SELECT a = 1 OR (SELECT 3 WHERE a = a) = 3));
+a
+1
+EXPLAIN EXTENDED
+SELECT * FROM t1 WHERE a = 1 AND
+(3 = 0 OR (SELECT a = 1 OR (SELECT 3 WHERE a = a) = 3));
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	3	100.00	Using where; Using temporary
+3	DEPENDENT SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
+Warnings:
+Note	1276	Field or reference 'test.t1.a' of SELECT #2 was resolved in SELECT #1
+Note	1276	Field or reference 'test.t1.a' of SELECT #3 was resolved in SELECT #1
+Note	1276	Field or reference 'test.t1.a' of SELECT #3 was resolved in SELECT #1
+Note	1249	Select 2 was reduced during optimization
+Note	1003	/* select#1 */ select `test`.`t1`.`a` AS `a` from `test`.`t1` where `test`.`t1`.`a` = 1 and (1 or <expr_cache><`test`.`t1`.`a`>((/* select#3 */ select 3 from DUAL  where `test`.`t1`.`a` = `test`.`t1`.`a`)) = 3)
+PREPARE stmt FROM 'SELECT * FROM t1 WHERE a = 1 AND
+  (3 = 0 OR (SELECT a = 1 OR (SELECT 3 WHERE a = a) = 3))';
+EXECUTE stmt;
+a
+1
+EXECUTE stmt;
+a
+1
+CREATE VIEW v1 AS SELECT * FROM t1 WHERE a = 1 AND
+(3 = 0 OR (SELECT a = 1 OR (SELECT 3 WHERE a = a) = 3));
+SELECT * FROM v1;
+a
+1
+# Test for nested AND conditions:
+SELECT * FROM t1 WHERE a = 1 OR
+(3 = 3 AND (SELECT a = 1 AND (SELECT 3 WHERE a = a) = 3));
+a
+1
+PREPARE stmt FROM 'SELECT * FROM t1 WHERE a = 1 OR
+  (3 = 3 AND (SELECT a = 1 AND (SELECT 3 WHERE a = a) = 3))';
+EXECUTE stmt;
+a
+1
+EXECUTE stmt;
+a
+1
+CREATE VIEW v2 AS SELECT * FROM t1 WHERE a = 1 OR
+(3 = 3 AND (SELECT a = 1 AND (SELECT 3 WHERE a = a) = 3));
+SELECT * FROM v2;
+a
+1
+DROP TABLE t1;
+DROP VIEW v1, v2;
 End of 10.0 tests
 set join_cache_level=default;
 set @@optimizer_switch=@save_optimizer_switch_jcl6;

mysql-test/main/select_pkeycache.result

@@ -5639,4 +5639,60 @@ EXECUTE stmt;
 COUNT(DISTINCT a)
 3
 DROP TABLE t1;
+#
+# MDEV-29294: Assertion `functype() == ((Item_cond *) new_item)->functype()'
+#             failed in Item_cond::remove_eq_conds on SELECT
+#
+CREATE TABLE t1 (a INT);
+INSERT INTO t1 VALUES (1),(2),(3);
+# Test for nested OR conditions:
+SELECT * FROM t1 WHERE a = 1 AND
+(3 = 0 OR (SELECT a = 1 OR (SELECT 3 WHERE a = a) = 3));
+a
+1
+EXPLAIN EXTENDED
+SELECT * FROM t1 WHERE a = 1 AND
+(3 = 0 OR (SELECT a = 1 OR (SELECT 3 WHERE a = a) = 3));
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	3	100.00	Using where; Using temporary
+3	DEPENDENT SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
+Warnings:
+Note	1276	Field or reference 'test.t1.a' of SELECT #2 was resolved in SELECT #1
+Note	1276	Field or reference 'test.t1.a' of SELECT #3 was resolved in SELECT #1
+Note	1276	Field or reference 'test.t1.a' of SELECT #3 was resolved in SELECT #1
+Note	1249	Select 2 was reduced during optimization
+Note	1003	/* select#1 */ select `test`.`t1`.`a` AS `a` from `test`.`t1` where `test`.`t1`.`a` = 1 and (1 or <expr_cache><`test`.`t1`.`a`>((/* select#3 */ select 3 from DUAL  where `test`.`t1`.`a` = `test`.`t1`.`a`)) = 3)
+PREPARE stmt FROM 'SELECT * FROM t1 WHERE a = 1 AND
+  (3 = 0 OR (SELECT a = 1 OR (SELECT 3 WHERE a = a) = 3))';
+EXECUTE stmt;
+a
+1
+EXECUTE stmt;
+a
+1
+CREATE VIEW v1 AS SELECT * FROM t1 WHERE a = 1 AND
+(3 = 0 OR (SELECT a = 1 OR (SELECT 3 WHERE a = a) = 3));
+SELECT * FROM v1;
+a
+1
+# Test for nested AND conditions:
+SELECT * FROM t1 WHERE a = 1 OR
+(3 = 3 AND (SELECT a = 1 AND (SELECT 3 WHERE a = a) = 3));
+a
+1
+PREPARE stmt FROM 'SELECT * FROM t1 WHERE a = 1 OR
+  (3 = 3 AND (SELECT a = 1 AND (SELECT 3 WHERE a = a) = 3))';
+EXECUTE stmt;
+a
+1
+EXECUTE stmt;
+a
+1
+CREATE VIEW v2 AS SELECT * FROM t1 WHERE a = 1 OR
+(3 = 3 AND (SELECT a = 1 AND (SELECT 3 WHERE a = a) = 3));
+SELECT * FROM v2;
+a
+1
+DROP TABLE t1;
+DROP VIEW v1, v2;
 End of 10.0 tests

sql/item_cmpfunc.cc

@@ -4816,38 +4816,18 @@ Item_cond::fix_fields(THD *thd, Item **ref)
 
   if (check_stack_overrun(thd, STACK_MIN_SIZE, buff))
     return TRUE;				// Fatal error flag is set!
-  /*
-    The following optimization reduces the depth of an AND-OR tree.
-    E.g. a WHERE clause like
-      F1 AND (F2 AND (F2 AND F4))
-    is parsed into a tree with the same nested structure as defined
-    by braces. This optimization will transform such tree into
-      AND (F1, F2, F3, F4).
-    Trees of OR items are flattened as well:
-      ((F1 OR F2) OR (F3 OR F4))   =>   OR (F1, F2, F3, F4)
-    Items for removed AND/OR levels will dangle until the death of the
-    entire statement.
-    The optimization is currently prepared statements and stored procedures
-    friendly as it doesn't allocate any memory and its effects are durable
-    (i.e. do not depend on PS/SP arguments).
-  */
-  while ((item=li++))
+
+  while (li++)
   {
-    while (item->type() == Item::COND_ITEM &&
-	   ((Item_cond*) item)->functype() == functype() &&
-           !((Item_cond*) item)->list.is_empty())
-    {						// Identical function
-      li.replace(((Item_cond*) item)->list);
-      ((Item_cond*) item)->list.empty();
-      item= *li.ref();				// new current item
-    }
+    merge_sub_condition(li);
+    item= *li.ref();
     if (abort_on_null)
       item->top_level_item();
 
     /*
       replace degraded condition:
         was:    <field>
-        become: <field> = 1
+        become: <field> != 0
     */
     Item::Type type= item->type();
     if (type == Item::FIELD_ITEM || type == Item::REF_ITEM)
@@ -4863,7 +4843,9 @@ Item_cond::fix_fields(THD *thd, Item **ref)
 
     if (item->fix_fields_if_needed_for_bool(thd, li.ref()))
       return TRUE; /* purecov: inspected */
-    item= *li.ref(); // item can be substituted in fix_fields
+    merge_sub_condition(li);
+    item= *li.ref(); // may be substituted in fix_fields/merge_item_if_possible
+
     used_tables_cache|=     item->used_tables();
     if (item->const_item() && !item->with_param &&
         !item->is_expensive() && !cond_has_datetime_is_null(item))
@@ -4915,6 +4897,55 @@ Item_cond::fix_fields(THD *thd, Item **ref)
   return FALSE;
 }
 
+/**
+  @brief
+  Merge a lower-level condition pointed by the iterator into this Item_cond
+  if possible
+
+  @param li         list iterator pointing to condition that must be
+                    examined and merged if possible.
+
+  @details
+  If an item pointed by the iterator is an instance of Item_cond with the
+  same functype() as this Item_cond (i.e. both are Item_cond_and or both are
+  Item_cond_or) then the arguments of that lower-level item can be merged
+  into the list of arguments of this upper-level Item_cond.
+
+  This optimization reduces the depth of an AND-OR tree.
+  E.g. a WHERE clause like
+    F1 AND (F2 AND (F2 AND F4))
+  is parsed into a tree with the same nested structure as defined
+  by braces. This optimization will transform such tree into
+    AND (F1, F2, F3, F4).
+  Trees of OR items are flattened as well:
+    ((F1 OR F2) OR (F3 OR F4))   =>   OR (F1, F2, F3, F4)
+  Items for removed AND/OR levels will dangle until the death of the
+  entire statement.
+
+  The optimization is currently prepared statements and stored procedures
+  friendly as it doesn't allocate any memory and its effects are durable
+  (i.e. do not depend on PS/SP arguments).
+*/
+void Item_cond::merge_sub_condition(List_iterator<Item>& li)
+{
+  Item *item= *li.ref();
+
+  /*
+    The check for list.is_empty() is to catch empty Item_cond_and() items.
+    We may encounter Item_cond_and with an empty list, because optimizer code
+    strips multiple equalities, combines items, then adds multiple equalities
+    back
+  */
+  while (item->type() == Item::COND_ITEM &&
+         ((Item_cond*) item)->functype() == functype() &&
+         !((Item_cond*) item)->list.is_empty())
+  {
+    li.replace(((Item_cond*) item)->list);
+    ((Item_cond*) item)->list.empty();
+    item= *li.ref();
+  }
+}
+
 
 bool
 Item_cond::eval_not_null_tables(void *opt_arg)

sql/item_cmpfunc.h

@@ -3046,6 +3046,9 @@ class Item_cond :public Item_bool_func
   Item *build_clone(THD *thd);
   bool excl_dep_on_table(table_map tab_map);
   bool excl_dep_on_grouping_fields(st_select_lex *sel);
+
+private:
+  void merge_sub_condition(List_iterator<Item>& li);
 };
 
 template <template<class> class LI, class T> class Item_equal_iterator;