MDEV-35168 subselects with outer references to derived tables may be …

mysql-test/main/subselect4.result

@@ -3373,4 +3373,50 @@ CREATE TABLE t(c INT);
 SELECT (SELECT 0 GROUP BY c HAVING (SELECT c)) FROM t GROUP BY c;
 (SELECT 0 GROUP BY c HAVING (SELECT c))
 DROP TABLE t;
+#
+# MDEV-35168 subselects with outer references to derived tables may be incorrectly evaluated as constant
+#
+create table t1 (a int);
+insert into t1 (a) values (5);
+select 1 as one from
+(
+t1 as t2 left join
+(
+select 0 as c1
+from t1
+) as dt1
+on dt1.c1 = t2.a
+)
+where exists
+(
+select 1 from t1
+where dt1.c1 <> t1.a
+);
+one
+create view v1 as ( select 0 as c1 from t1 );
+select 1 as one from
+(
+t1 left join v1
+on v1.c1 = t1.a
+)
+where exists
+(
+select 1 from t1
+where v1.c1 <> t1.a
+);
+one
+with cte1 as ( select 0 as c1 from t1 )
+select 1 as one from
+(
+t1 left join cte1
+on cte1.c1 = t1.a
+)
+where exists
+(
+select 1 from t1
+where cte1.c1 <> t1.a
+);
+one
+drop view v1;
+drop table t1;
 # End of 10.11 tests

mysql-test/main/subselect4.test

@@ -2695,4 +2695,54 @@ CREATE TABLE t(c INT);
 SELECT (SELECT 0 GROUP BY c HAVING (SELECT c)) FROM t GROUP BY c;
 DROP TABLE t;
 
+--echo #
+--echo # MDEV-35168 subselects with outer references to derived tables may be incorrectly evaluated as constant
+--echo #
+
+create table t1 (a int);
+insert into t1 (a) values (5);
+
+select 1 as one from
+  (
+    t1 as t2 left join
+    (
+      select 0 as c1
+        from t1
+    ) as dt1
+      on dt1.c1 = t2.a
+  )
+  where exists
+  (
+    select 1 from t1
+      where dt1.c1 <> t1.a
+  );
+
+create view v1 as ( select 0 as c1 from t1 );
+
+select 1 as one from
+  (
+    t1 left join v1
+      on v1.c1 = t1.a
+  )
+  where exists
+  (
+    select 1 from t1
+      where v1.c1 <> t1.a
+  );
+
+with cte1 as ( select 0 as c1 from t1 )
+select 1 as one from
+  (
+    t1 left join cte1
+      on cte1.c1 = t1.a
+  )
+  where exists
+  (
+    select 1 from t1
+      where cte1.c1 <> t1.a
+  );
+
+drop view v1;
+drop table t1;
+
 --echo # End of 10.11 tests

sql/item.cc

@@ -3274,6 +3274,21 @@ bool Item_field::enumerate_field_refs_processor(void *arg)
   return FALSE;
 }
 
+
+bool Item_direct_view_ref::enumerate_table_refs_processor(void *arg)
+{
+  Field_fixer *ff= (Field_fixer*)arg;
+  st_select_lex *cmp= ff->new_parent->get_merged_into();
+
+  // our table is resolved in the select of interest
+  if (null_ref_table &&
+      null_ref_table != NO_NULL_TABLE &&
+      null_ref_table->pos_in_table_list->select_lex == cmp)
+    ff->used_tables |= null_ref_table->map;
+  return FALSE;
+}
+
+
 bool Item_field::update_table_bitmaps_processor(void *arg)
 {
   update_table_bitmaps();

sql/item.h

@@ -2303,6 +2303,7 @@ class Item :public Value_source,
   virtual bool update_table_bitmaps_processor(void *arg) { return 0; }
 
   virtual bool enumerate_field_refs_processor(void *arg) { return 0; }
+  virtual bool enumerate_table_refs_processor(void *arg) { return 0; }
   virtual bool mark_as_eliminated_processor(void *arg) { return 0; }
   virtual bool eliminate_subselect_processor(void *arg) { return 0; }
   virtual bool view_used_tables_processor(void *arg) { return 0; }
@@ -6342,6 +6343,7 @@ class Item_direct_view_ref :public Item_direct_ref
       set_null_ref_table();
   }
 
+  bool enumerate_table_refs_processor(void *arg) override;
   bool fix_fields(THD *, Item **) override;
   bool eq(const Item *item, const Eq_config &config) const override;
   Item *get_tmp_table_item(THD *thd) override
@@ -8351,4 +8353,24 @@ inline void TABLE::use_all_stored_columns()
       bitmap_clear_bit(read_set, (*vf)->field_index);
 }
 
+
+class Field_fixer: public Field_enumerator
+{
+public:
+  table_map used_tables; /* Collect used_tables here */
+  st_select_lex *new_parent; /* Select we're in */
+  void visit_field(Item_field *item) override
+  {
+    //for (TABLE_LIST *tbl= new_parent->leaf_tables; tbl; tbl= tbl->next_local)
+    //{
+    //  if (tbl->table == field->table)
+    //  {
+        used_tables|= item->field->table->map;
+    //    return;
+    //  }
+    //}
+    //used_tables |= OUTER_REF_TABLE_BIT;
+  }
+};
+
 #endif /* SQL_ITEM_INCLUDED */

sql/item_subselect.cc

@@ -469,26 +469,6 @@ void Item_subselect::fix_after_pullout(st_select_lex *new_parent,
 }
 
 
-class Field_fixer: public Field_enumerator
-{
-public:
-  table_map used_tables; /* Collect used_tables here */
-  st_select_lex *new_parent; /* Select we're in */
-  void visit_field(Item_field *item) override
-  {
-    //for (TABLE_LIST *tbl= new_parent->leaf_tables; tbl; tbl= tbl->next_local)
-    //{
-    //  if (tbl->table == field->table)
-    //  {
-        used_tables|= item->field->table->map;
-    //    return;
-    //  }
-    //}
-    //used_tables |= OUTER_REF_TABLE_BIT;
-  }
-};
-
-
 /*
   Recalculate used_tables_cache 
 */
@@ -538,6 +518,14 @@ void Item_subselect::recalc_used_tables(st_select_lex *new_parent,
           fixer.used_tables= 0;
           fixer.new_parent= new_parent;
           upper->item->walk(&Item::enumerate_field_refs_processor, 0, &fixer);
+          /*
+            An reference (that can be null) might refer to a constant item
+            (that isn't and can't be null).
+            We need to update the table map to include tables that might be
+            null to avoid this subselect being marked as constant.
+            This information is in the Item_direct_view_ref wrapper.
+          */
+          upper->item->walk(&Item::enumerate_table_refs_processor, 0, &fixer);
           used_tables_cache |= fixer.used_tables;
           upper->item->walk(&Item::update_table_bitmaps_processor, FALSE, NULL);
 /*

sql/sql_lex.h

@@ -1714,6 +1714,16 @@ class st_select_lex: public st_select_lex_node
   TABLE_LIST *find_table(THD *thd,
                          const LEX_CSTRING *db_name,
                          const LEX_CSTRING *table_name);
+
+  st_select_lex *get_merged_into()
+  {
+    st_select_lex *ret= this;
+
+    while(ret->merged_into)
+      ret= ret->merged_into;
+
+    return ret;
+  }
 };
 typedef class st_select_lex SELECT_LEX;