Problem was that for cases like:

SELECT ... WHERE XX IN (SELECT YY)
this was transformed to something like:
SELECT ... WHERE IF_EXISTS(SELECT ... HAVING XX=YY)

The bug was that for normal execution XX was fixed in the original outer SELECT context while in PS it was fixed in the sub query context and this confused the optimizer.

Fixed by ensuring that XX is always fixed in the outer context.

mysql-test/r/subselect_mat.result

@@ -2145,6 +2145,33 @@ drop database mysqltest1;
 drop database mysqltest2;
 drop database mysqltest3;
 drop database mysqltest4;
+#
+# MDEV-7810 Wrong result on execution of a query as a PS
+# (both 1st and further executions)
+CREATE TABLE t1 (a INT NOT NULL) ENGINE=MyISAM;
+INSERT INTO t1 VALUES (0),(8);
+SELECT DISTINCT t9.* FROM t1 AS t9, t1 AS t2;
+a
+0
+8
+SELECT MIN(t3.a) FROM ( t1 AS t3 INNER JOIN t1 AS t4 ON (t3.a = t4.a));
+MIN(t3.a)
+0
+SELECT a FROM ( SELECT DISTINCT t9.* FROM t1 AS t9, t1 AS t2 ) AS sq 
+WHERE a IN ( SELECT MIN(t3.a) FROM ( t1 AS t3 INNER JOIN t1 AS t4 ON (t3.a = t4.a) ) );
+a
+0
+PREPARE stmt FROM "
+SELECT a FROM ( SELECT DISTINCT t9.* FROM t1 AS t9, t1 AS t2 ) AS sq 
+WHERE a IN ( SELECT MIN(t3.a) FROM ( t1 AS t3 INNER JOIN t1 AS t4 ON (t3.a = t4.a) ) )
+";
+execute stmt;
+a
+0
+execute stmt;
+a
+0
+drop table t1;
 # End of 5.5 tests
 set @subselect_mat_test_optimizer_switch_value=null;
 set @@optimizer_switch='materialization=on,in_to_exists=off,semijoin=off';

mysql-test/r/subselect_sj_mat.result

@@ -2185,4 +2185,31 @@ drop database mysqltest1;
 drop database mysqltest2;
 drop database mysqltest3;
 drop database mysqltest4;
+#
+# MDEV-7810 Wrong result on execution of a query as a PS
+# (both 1st and further executions)
+CREATE TABLE t1 (a INT NOT NULL) ENGINE=MyISAM;
+INSERT INTO t1 VALUES (0),(8);
+SELECT DISTINCT t9.* FROM t1 AS t9, t1 AS t2;
+a
+0
+8
+SELECT MIN(t3.a) FROM ( t1 AS t3 INNER JOIN t1 AS t4 ON (t3.a = t4.a));
+MIN(t3.a)
+0
+SELECT a FROM ( SELECT DISTINCT t9.* FROM t1 AS t9, t1 AS t2 ) AS sq 
+WHERE a IN ( SELECT MIN(t3.a) FROM ( t1 AS t3 INNER JOIN t1 AS t4 ON (t3.a = t4.a) ) );
+a
+0
+PREPARE stmt FROM "
+SELECT a FROM ( SELECT DISTINCT t9.* FROM t1 AS t9, t1 AS t2 ) AS sq 
+WHERE a IN ( SELECT MIN(t3.a) FROM ( t1 AS t3 INNER JOIN t1 AS t4 ON (t3.a = t4.a) ) )
+";
+execute stmt;
+a
+0
+execute stmt;
+a
+0
+drop table t1;
 # End of 5.5 tests

mysql-test/t/subselect_sj_mat.test

@@ -1841,5 +1841,24 @@ drop database mysqltest2;
 drop database mysqltest3;
 drop database mysqltest4;
 
---echo # End of 5.5 tests
+--echo #
+--echo # MDEV-7810 Wrong result on execution of a query as a PS
+--echo # (both 1st and further executions)
+
+CREATE TABLE t1 (a INT NOT NULL) ENGINE=MyISAM;
+INSERT INTO t1 VALUES (0),(8);
+
+SELECT DISTINCT t9.* FROM t1 AS t9, t1 AS t2;
+SELECT MIN(t3.a) FROM ( t1 AS t3 INNER JOIN t1 AS t4 ON (t3.a = t4.a));
+SELECT a FROM ( SELECT DISTINCT t9.* FROM t1 AS t9, t1 AS t2 ) AS sq 
+WHERE a IN ( SELECT MIN(t3.a) FROM ( t1 AS t3 INNER JOIN t1 AS t4 ON (t3.a = t4.a) ) );
+PREPARE stmt FROM "
+SELECT a FROM ( SELECT DISTINCT t9.* FROM t1 AS t9, t1 AS t2 ) AS sq 
+WHERE a IN ( SELECT MIN(t3.a) FROM ( t1 AS t3 INNER JOIN t1 AS t4 ON (t3.a = t4.a) ) )
+";
+execute stmt;
+execute stmt;
 
+drop table t1;
+
+--echo # End of 5.5 tests

sql/item_subselect.cc

@@ -1999,12 +1999,31 @@ Item_in_subselect::create_single_in_to_exists_cond(JOIN * join,
     during JOIN::optimize: this->tmp_having= this->having; this->having= 0;
   */
   Item* join_having= join->having ? join->having : join->tmp_having;
-
   DBUG_ENTER("Item_in_subselect::create_single_in_to_exists_cond");
 
   *where_item= NULL;
   *having_item= NULL;
 
+  /*
+    For PS we have to do fix_fields(expr) here to ensure that it's
+    evaluated in the outer context.  If not, then fix_having() will do
+    a fix_fields(expr) in the inner context and mark expr as
+    'depended', which will cause update_ref_and_keys() to find wrong
+    keys.
+    When not running PS, fix_fields(expr) as already been done earlier and
+    the following test does nothing.
+  */
+  if (expr && !expr->fixed)
+  {
+    SELECT_LEX *save_current_select= thd->lex->current_select;
+    thd->lex->current_select= thd->lex->current_select->outer_select();
+    bool tmp;
+    tmp= expr->fix_fields(thd, 0);
+    thd->lex->current_select= save_current_select;
+    if (tmp)
+      DBUG_RETURN(true);
+  }
+
   if (join_having || select_lex->with_sum_func ||
       select_lex->group_list.elements)
   {

sql/sql_base.cc

@@ -6859,6 +6859,7 @@ find_field_in_tables(THD *thd, Item_ident *item,
 
   if (item->cached_table)
   {
+    DBUG_PRINT("info", ("using cached table"));
     /*
       This shortcut is used by prepared statements. We assume that
       TABLE_LIST *first_table is not changed during query execution (which
@@ -6935,8 +6936,6 @@ find_field_in_tables(THD *thd, Item_ident *item,
       return found;
     }
   }
-  else
-    item->can_be_depended= TRUE;
 
   if (db && lower_case_table_names)
   {

sql/sql_select.cc

@@ -4904,6 +4904,8 @@ update_ref_and_keys(THD *thd, DYNAMIC_ARRAY *keyuse,JOIN_TAB *join_tab,
   KEY_FIELD *key_fields, *end, *field;
   uint sz;
   uint m= max(select_lex->max_equal_elems,1);
+  DBUG_ENTER("update_ref_and_keys");
+  DBUG_PRINT("enter", ("normal_tables: %llx", normal_tables));
 
   SELECT_LEX *sel=thd->lex->current_select; 
   sel->cond_count= 0;
@@ -4950,7 +4952,7 @@ update_ref_and_keys(THD *thd, DYNAMIC_ARRAY *keyuse,JOIN_TAB *join_tab,
   sz= max(sizeof(KEY_FIELD),sizeof(SARGABLE_PARAM))*
     ((sel->cond_count*2 + sel->between_count)*m+1);
   if (!(key_fields=(KEY_FIELD*)	thd->alloc(sz)))
-    return TRUE; /* purecov: inspected */
+    DBUG_RETURN(TRUE); /* purecov: inspected */
   and_level= 0;
   field= end= key_fields;
   *sargables= (SARGABLE_PARAM *) key_fields + 
@@ -4959,7 +4961,7 @@ update_ref_and_keys(THD *thd, DYNAMIC_ARRAY *keyuse,JOIN_TAB *join_tab,
   (*sargables)[0].field= 0; 
 
   if (my_init_dynamic_array(keyuse,sizeof(KEYUSE),20,64))
-    return TRUE;
+    DBUG_RETURN(TRUE);
 
   if (cond)
   {
@@ -5009,16 +5011,16 @@ update_ref_and_keys(THD *thd, DYNAMIC_ARRAY *keyuse,JOIN_TAB *join_tab,
   for ( ; field != end ; field++)
   {
     if (add_key_part(keyuse,field))
-      return TRUE;
+      DBUG_RETURN(TRUE);
   }
 
   if (select_lex->ftfunc_list->elements)
   {
     if (add_ft_keys(keyuse,join_tab,cond,normal_tables))
-      return TRUE;
+      DBUG_RETURN(TRUE);
   }
 
-  return FALSE;
+  DBUG_RETURN(FALSE);
 }