MDEV-25080 Implement ColumnStore-side changes for pushdown of SELECT_LEX_UNITs.

dbcon/mysql/ha_mcs.cpp

@@ -45,7 +45,8 @@ group_by_handler* create_columnstore_group_by_handler(THD* thd, Query* query);
 
 derived_handler* create_columnstore_derived_handler(THD* thd, TABLE_LIST* derived);
 
-select_handler* create_columnstore_select_handler(THD* thd, SELECT_LEX* sel);
+select_handler* create_columnstore_select_handler(THD* thd, SELECT_LEX* sel_lex, SELECT_LEX_UNIT* sel_unit);
+select_handler* create_columnstore_unit_handler(THD* thd, SELECT_LEX_UNIT* sel_unit);
 
 /* Variables for example share methods */
 
@@ -1835,6 +1836,7 @@ static int columnstore_init_func(void* p)
   mcs_hton->create_group_by = create_columnstore_group_by_handler;
   mcs_hton->create_derived = create_columnstore_derived_handler;
   mcs_hton->create_select = create_columnstore_select_handler;
+  mcs_hton->create_unit = create_columnstore_unit_handler;
   mcs_hton->db_type = DB_TYPE_AUTOASSIGN;
 
 #ifdef HAVE_PSI_INTERFACE

dbcon/mysql/ha_mcs_execplan.cpp

@@ -6681,7 +6681,8 @@ void setExecutionParams(gp_walk_info& gwi, SCSEP& csep)
  * RETURNS
  *  error id as an int
  ***********************************************************/
-int processFrom(bool& isUnion, SELECT_LEX& select_lex, gp_walk_info& gwi, SCSEP& csep)
+int processFrom(bool& isUnion, SELECT_LEX& select_lex, gp_walk_info& gwi, SCSEP& csep,
+                bool isSelectHandlerTop, bool isSelectLexUnit)
 {
   // populate table map and trigger syscolumn cache for all the tables (@bug 1637).
   // all tables on FROM list must have at least one col in colmap
@@ -6820,7 +6821,7 @@ int processFrom(bool& isUnion, SELECT_LEX& select_lex, gp_walk_info& gwi, SCSEP&
   // Existed pushdown handlers won't get in this scope
   // except UNION pushdown that is to come.
   // is_unit_op() give a segv for derived_handler's SELECT_LEX
-  if (!isUnion && select_lex.master_unit()->is_unit_op())
+  if (!isUnion && (!isSelectHandlerTop || isSelectLexUnit) && select_lex.master_unit()->is_unit_op())
   {
     // MCOL-2178 isUnion member only assigned, never used
     // MIGR::infinidb_vtable.isUnion = true;
@@ -7378,7 +7379,8 @@ void buildInToExistsFilter(gp_walk_info& gwi, SELECT_LEX& select_lex)
  *  error id as an int
  ***********************************************************/
 int getSelectPlan(gp_walk_info& gwi, SELECT_LEX& select_lex, SCSEP& csep, bool isUnion,
-                  bool isSelectHandlerTop, const std::vector<COND*>& condStack)
+                  bool isSelectHandlerTop, bool isSelectLexUnit,
+                  const std::vector<COND*>& condStack)
 {
 #ifdef DEBUG_WALK_COND
   cerr << "getSelectPlan()" << endl;
@@ -7406,7 +7408,8 @@ int getSelectPlan(gp_walk_info& gwi, SELECT_LEX& select_lex, SCSEP& csep, bool i
   CalpontSelectExecutionPlan::SelectList derivedTbList;
   // @bug 1796. Remember table order on the FROM list.
   gwi.clauseType = FROM;
-  if ((rc = processFrom(isUnion, select_lex, gwi, csep)))
+  if ((rc = processFrom(isUnion, select_lex, gwi, csep, isSelectHandlerTop,
+                        isSelectLexUnit)))
   {
     return rc;
   }
@@ -8799,9 +8802,10 @@ int cs_get_derived_plan(ha_columnstore_derived_handler* handler, THD* thd, SCSEP
   return 0;
 }
 
-int cs_get_select_plan(ha_columnstore_select_handler* handler, THD* thd, SCSEP& csep, gp_walk_info& gwi)
+int cs_get_select_plan(ha_columnstore_select_handler* handler, THD* thd, SCSEP& csep, gp_walk_info& gwi,
+                       bool isSelectLexUnit)
 {
-  SELECT_LEX& select_lex = *handler->select;
+  SELECT_LEX& select_lex = handler->select_lex ? *handler->select_lex : *handler->lex_unit->first_select();
 
   if (select_lex.where)
   {
@@ -8813,7 +8817,7 @@ int cs_get_select_plan(ha_columnstore_select_handler* handler, THD* thd, SCSEP&
   convertOuterJoinToInnerJoin(&select_lex.top_join_list, gwi.tableOnExprList, gwi.condList,
                               handler->tableOuterJoinMap);
 
-  int status = getSelectPlan(gwi, select_lex, csep, false, true);
+  int status = getSelectPlan(gwi, select_lex, csep, false, true, isSelectLexUnit);
 
   if (status > 0)
     return ER_INTERNAL_ERROR;

dbcon/mysql/ha_mcs_impl.cpp

@@ -1392,7 +1392,7 @@ uint32_t doUpdateDelete(THD* thd, gp_walk_info& gwi, const std::vector<COND*>& c
 
     gwi.clauseType = WHERE;
 
-    if (getSelectPlan(gwi, select_lex, updateCP, false, false, condStack) !=
+    if (getSelectPlan(gwi, select_lex, updateCP, false, false, false, condStack) !=
         0)  //@Bug 3030 Modify the error message for unsupported functions
     {
       if (gwi.cs_vtable_is_update_with_derive)
@@ -4886,7 +4886,7 @@ int ha_mcs_impl_group_by_end(TABLE* table)
  * RETURN:
  *    rc as int
  ***********************************************************/
-int ha_mcs_impl_pushdown_init(mcs_handler_info* handler_info, TABLE* table)
+int ha_mcs_impl_pushdown_init(mcs_handler_info* handler_info, TABLE* table, bool isSelectLexUnit)
 {
   IDEBUG(cout << "pushdown_init for table " << endl);
   THD* thd = current_thd;
@@ -5076,7 +5076,7 @@ int ha_mcs_impl_pushdown_init(mcs_handler_info* handler_info, TABLE* table)
       if (handler_info->hndl_type == mcs_handler_types_t::SELECT)
       {
         sh = reinterpret_cast<ha_columnstore_select_handler*>(handler_info->hndl_ptr);
-        status = cs_get_select_plan(sh, thd, csep, gwi);
+        status = cs_get_select_plan(sh, thd, csep, gwi, isSelectLexUnit);
       }
       else if (handler_info->hndl_type == DERIVED)
       {

dbcon/mysql/ha_mcs_impl.h

@@ -44,7 +44,7 @@ extern int ha_mcs_impl_direct_update_delete_rows(bool execute, ha_rows* affected
                                                  const std::vector<COND*>& condStack);
 extern int ha_mcs_impl_delete_row();
 extern int ha_mcs_impl_rnd_pos(uchar* buf, uchar* pos);
-extern int ha_mcs_impl_pushdown_init(mcs_handler_info* handler_info, TABLE* table);
+extern int ha_mcs_impl_pushdown_init(mcs_handler_info* handler_info, TABLE* table, bool isSelectLexUnit = false);
 extern int ha_mcs_impl_select_next(uchar* buf, TABLE* table, long timeZone);
 extern int ha_mcs_impl_group_by_init(mcs_handler_info* handler_info, TABLE* table);
 extern int ha_mcs_impl_group_by_next(TABLE* table, long timeZone);

dbcon/mysql/ha_mcs_impl_if.h

@@ -397,9 +397,9 @@ int cp_get_group_plan(THD* thd, execplan::SCSEP& csep, cal_impl_if::cal_group_in
 int cs_get_derived_plan(ha_columnstore_derived_handler* handler, THD* thd, execplan::SCSEP& csep,
                         gp_walk_info& gwi);
 int cs_get_select_plan(ha_columnstore_select_handler* handler, THD* thd, execplan::SCSEP& csep,
-                       gp_walk_info& gwi);
+                       gp_walk_info& gwi, bool isSelectLexUnit);
 int getSelectPlan(gp_walk_info& gwi, SELECT_LEX& select_lex, execplan::SCSEP& csep, bool isUnion = false,
-                  bool isSelectHandlerTop = false,
+                  bool isSelectHandlerTop = false, bool isSelectLexUnit = false,
                   const std::vector<COND*>& condStack = std::vector<COND*>());
 int getGroupPlan(gp_walk_info& gwi, SELECT_LEX& select_lex, execplan::SCSEP& csep, cal_group_info& gi,
                  bool isUnion = false);

dbcon/mysql/ha_mcs_pushdown.cpp

@@ -728,20 +728,22 @@ int ha_mcs_group_by_handler::end_scan()
   DBUG_RETURN(rc);
 }
 
-/*@brief  create_columnstore_select_handler- Creates handler*/
+/*@brief  create_columnstore_select_handler_- Creates handler
-/************************************************************
+************************************************************
  * DESCRIPTION:
  * Creates a select handler if there is no non-equi JOIN, e.g
  * t1.c1 > t2.c2 and logical OR in the filter predicates.
  * More details in server/sql/select_handler.h
  * PARAMETERS:
  *    thd - THD pointer.
- *    select_lex - SELECT_LEX* that describes the query.
+ *    sel_lex - SELECT_LEX* that describes the query.
+ *    sel_unit - SELECT_LEX_UNIT* that describes the query.
+ *    Only one of sel_lex and sel_unit is not null.
  * RETURN:
  *    select_handler if possible
  *    NULL in other case
  ***********************************************************/
-select_handler* create_columnstore_select_handler(THD* thd, SELECT_LEX* select_lex)
+select_handler* create_columnstore_select_handler_(THD* thd, SELECT_LEX* sel_lex, SELECT_LEX_UNIT* sel_unit)
 {
   mcs_select_handler_mode_t select_handler_mode = get_select_handler_mode(thd);
 
@@ -778,60 +780,96 @@ select_handler* create_columnstore_select_handler(THD* thd, SELECT_LEX* select_l
     return nullptr;
   }
 
-  // Iterate and traverse through the item list and the JOIN cond
+  std::vector<SELECT_LEX*> select_lex_vec;
-  // and do not create SH if the unsupported (set_user_var)
+
-  // function is present.
+  if (sel_unit && !sel_lex)
-  TABLE_LIST* table_ptr = select_lex->get_table_list();
-  for (; table_ptr; table_ptr = table_ptr->next_global)
   {
-    if (check_user_var(table_ptr->select_lex))
+    for (SELECT_LEX* sl = sel_unit->first_select(); sl; sl = sl->next_select())
     {
-      return nullptr;
+      select_lex_vec.push_back(sl);
+    }
+  }
+  else
+  {
+    select_lex_vec.push_back(sel_lex);
+  }
+
+  for (size_t i = 0; i < select_lex_vec.size(); i++)
+  {
+    SELECT_LEX* select_lex = select_lex_vec[i];
+
+    // Iterate and traverse through the item list and the JOIN cond
+    // and do not create SH if the unsupported (set_user_var)
+    // function is present.
+    TABLE_LIST* table_ptr = select_lex->get_table_list();
+    for (; table_ptr; table_ptr = table_ptr->next_global)
+    {
+      if (check_user_var(table_ptr->select_lex))
+      {
+        return nullptr;
+      }
     }
   }
 
   // We apply dedicated rewrites from MDB here so MDB's data structures
   // becomes dirty and CS has to raise an error in case of any problem
   // or unsupported feature.
-  ha_columnstore_select_handler* handler = new ha_columnstore_select_handler(thd, select_lex);
+  ha_columnstore_select_handler* handler;
 
-  JOIN* join = select_lex->join;
+  if (sel_unit && sel_lex)
-
-  if (select_lex->first_cond_optimization && select_lex->handle_derived(thd->lex, DT_MERGE))
   {
-    if (!thd->is_error())
+    handler = new ha_columnstore_select_handler(thd, sel_lex, sel_unit);
-    {
+  }
-      my_printf_error(ER_INTERNAL_ERROR, "%s", MYF(0), "Error occured in select_lex::handle_derived()");
+  else if (sel_unit)
-    }
+  {
-
+    handler = new ha_columnstore_select_handler(thd, sel_unit);
-    return handler;
+  }
+  else
+  {
+    handler = new ha_columnstore_select_handler(thd, sel_lex);
   }
 
-  // This is partially taken from JOIN::optimize_inner() in sql/sql_select.cc
+  for (size_t i = 0; i < select_lex_vec.size(); i++)
-  if (select_lex->first_cond_optimization)
   {
-    create_explain_query_if_not_exists(thd->lex, thd->mem_root);
+    SELECT_LEX* select_lex = select_lex_vec[i];
-    Query_arena *arena, backup;
+    JOIN* join = select_lex->join;
-    arena = thd->activate_stmt_arena_if_needed(&backup);
-    COND* conds = join->conds;
-    select_lex->where = conds;
 
-    if (isPS)
+    if (select_lex->first_cond_optimization && select_lex->handle_derived(thd->lex, DT_MERGE))
     {
-      select_lex->prep_where = conds ? conds->copy_andor_structure(thd) : 0;
+      if (!thd->is_error())
+      {
+        my_printf_error(ER_INTERNAL_ERROR, "%s", MYF(0), "Error occured in select_lex::handle_derived()");
+      }
+
+      return handler;
     }
 
-    select_lex->update_used_tables();
+    // This is partially taken from JOIN::optimize_inner() in sql/sql_select.cc
+    if (select_lex->first_cond_optimization)
+    {
+      create_explain_query_if_not_exists(thd->lex, thd->mem_root);
+      Query_arena *arena, backup;
+      arena = thd->activate_stmt_arena_if_needed(&backup);
+      COND* conds = join->conds;
+      select_lex->where = conds;
 
-    if (arena)
+      if (isPS)
-      thd->restore_active_arena(arena, &backup);
+      {
+        select_lex->prep_where = conds ? conds->copy_andor_structure(thd) : 0;
+      }
+
+      select_lex->update_used_tables();
+
+      if (arena)
+        thd->restore_active_arena(arena, &backup);
 
 #ifdef DEBUG_WALK_COND
-    if (conds)
+      if (conds)
-    {
+      {
-      conds->traverse_cond(cal_impl_if::debug_walk, NULL, Item::POSTFIX);
+        conds->traverse_cond(cal_impl_if::debug_walk, NULL, Item::POSTFIX);
-    }
+      }
 #endif
+    }
   }
 
   // Attempt to execute the query using the select handler.
@@ -840,69 +878,45 @@ select_handler* create_columnstore_select_handler(THD* thd, SELECT_LEX* select_l
   // Skip execution for EXPLAIN queries
   if (!thd->lex->describe)
   {
-    // This is taken from JOIN::optimize()
+    for (size_t i = 0; i < select_lex_vec.size(); i++)
-    join->fields = &select_lex->item_list;
-
-    // Instantiate handler::table, which is the place for the result set.
-    if (handler->prepare())
     {
-      // check fallback
+      SELECT_LEX* select_lex = select_lex_vec[i];
-      if (select_handler_mode == mcs_select_handler_mode_t::AUTO)  // columnstore_select_handler=AUTO
+      JOIN* join = select_lex->join;
+
+      // This is taken from JOIN::optimize()
+      join->fields = &select_lex->item_list;
+
+      // Instantiate handler::table, which is the place for the result set.
+      if ((i == 0) && handler->prepare())
       {
-        push_warning(thd, Sql_condition::WARN_LEVEL_WARN, 9999,
+        // check fallback
-                     "MCS select_handler execution failed. Falling back to server execution");
+        if (select_handler_mode == mcs_select_handler_mode_t::AUTO)  // columnstore_select_handler=AUTO
-        restore_query_state(handler);
+        {
-        delete handler;
+          push_warning(thd, Sql_condition::WARN_LEVEL_WARN, 9999,
-        return nullptr;
+                       "MCS select_handler execution failed. Falling back to server execution");
+          restore_query_state(handler);
+          delete handler;
+          return nullptr;
+        }
+
+        // error out
+        if (!thd->is_error())
+        {
+          my_printf_error(ER_INTERNAL_ERROR, "%s", MYF(0), "Error occured in handler->prepare()");
+        }
+
+        return handler;
       }
 
-      // error out
+      // Prepare query execution
-      if (!thd->is_error())
+      // This is taken from JOIN::exec_inner()
-      {
+      if (!select_lex->outer_select() &&                             // (1)
-        my_printf_error(ER_INTERNAL_ERROR, "%s", MYF(0), "Error occured in handler->prepare()");
+          select_lex != select_lex->master_unit()->fake_select_lex)  // (2)
-      }
+        thd->lex->set_limit_rows_examined();
 
-      return handler;
+      if ((!sel_unit || sel_lex) && !join->tables_list &&
-    }
+          (join->table_count || !select_lex->with_sum_func) &&
-
+          !select_lex->have_window_funcs())
-    // Prepare query execution
-    // This is taken from JOIN::exec_inner()
-    if (!select_lex->outer_select() &&                             // (1)
-        select_lex != select_lex->master_unit()->fake_select_lex)  // (2)
-      thd->lex->set_limit_rows_examined();
-
-    if (!join->tables_list && (join->table_count || !select_lex->with_sum_func) &&
-        !select_lex->have_window_funcs())
-    {
-      if (!thd->is_error())
-      {
-        restore_query_state(handler);
-        delete handler;
-        return nullptr;
-      }
-
-      return handler;
-    }
-
-    if (!join->zero_result_cause && join->exec_const_cond && !join->exec_const_cond->val_int())
-      join->zero_result_cause = "Impossible WHERE noticed after reading const tables";
-
-    // We've called exec_const_cond->val_int(). This may have caused an error.
-    if (unlikely(thd->is_error()))
-    {
-      // error out
-      handler->pushdown_init_rc = 1;
-      return handler;
-    }
-
-    if (join->zero_result_cause)
-    {
-      if (join->select_lex->have_window_funcs() && join->send_row_on_empty_set())
-      {
-        join->const_tables = join->table_count;
-        join->first_select = sub_select_postjoin_aggr;
-      }
-      else
       {
         if (!thd->is_error())
         {
@@ -913,23 +927,56 @@ select_handler* create_columnstore_select_handler(THD* thd, SELECT_LEX* select_l
 
         return handler;
       }
-    }
 
-    if ((join->select_lex->options & OPTION_SCHEMA_TABLE) &&
+      if (!join->zero_result_cause && join->exec_const_cond && !join->exec_const_cond->val_int())
-        get_schema_tables_result(join, PROCESSED_BY_JOIN_EXEC))
+        join->zero_result_cause = "Impossible WHERE noticed after reading const tables";
-    {
+
-      if (!thd->is_error())
+      // We've called exec_const_cond->val_int(). This may have caused an error.
+      if (unlikely(thd->is_error()))
       {
-        my_printf_error(ER_INTERNAL_ERROR, "%s", MYF(0), "Error occured in get_schema_tables_result()");
+        // error out
+        handler->pushdown_init_rc = 1;
+        return handler;
       }
 
-      return handler;
+      if (join->zero_result_cause)
+      {
+        if (join->select_lex->have_window_funcs() && join->send_row_on_empty_set())
+        {
+          join->const_tables = join->table_count;
+          join->first_select = sub_select_postjoin_aggr;
+        }
+        else
+        {
+          if (!thd->is_error())
+          {
+            restore_query_state(handler);
+            delete handler;
+            return nullptr;
+          }
+
+          return handler;
+        }
+      }
+
+      if ((join->select_lex->options & OPTION_SCHEMA_TABLE) &&
+          get_schema_tables_result(join, PROCESSED_BY_JOIN_EXEC))
+      {
+        if (!thd->is_error())
+        {
+          my_printf_error(ER_INTERNAL_ERROR, "%s", MYF(0), "Error occured in get_schema_tables_result()");
+        }
+
+        return handler;
+      }
     }
 
     handler->scan_initialized = true;
     mcs_handler_info mhi(reinterpret_cast<void*>(handler), SELECT);
 
-    if ((handler->pushdown_init_rc = ha_mcs_impl_pushdown_init(&mhi, handler->table)))
+    bool isSelectLexUnit = (sel_unit && !sel_lex) ? true : false;
+
+    if ((handler->pushdown_init_rc = ha_mcs_impl_pushdown_init(&mhi, handler->table, isSelectLexUnit)))
     {
       // check fallback
       if (select_handler_mode == mcs_select_handler_mode_t::AUTO)
@@ -967,31 +1014,83 @@ select_handler* create_columnstore_select_handler(THD* thd, SELECT_LEX* select_l
       return handler;
     }
 
-    // Unset select_lex::first_cond_optimization
+    for (size_t i = 0; i < select_lex_vec.size(); i++)
-    if (select_lex->first_cond_optimization)
     {
-      first_cond_optimization_flag_toggle(select_lex, &first_cond_optimization_flag_unset);
+      SELECT_LEX* select_lex = select_lex_vec[i];
+
+      // Unset select_lex::first_cond_optimization
+      if (select_lex->first_cond_optimization)
+      {
+        first_cond_optimization_flag_toggle(select_lex, &first_cond_optimization_flag_unset);
+      }
     }
   }
 
   return handler;
 }
 
+select_handler* create_columnstore_select_handler(THD* thd, SELECT_LEX* select_lex, SELECT_LEX_UNIT* sel_unit)
+{
+  return create_columnstore_select_handler_(thd, select_lex, sel_unit);
+}
+
+select_handler* create_columnstore_unit_handler(THD* thd, SELECT_LEX_UNIT* sel_unit)
+{
+  return create_columnstore_select_handler_(thd, 0, sel_unit);
+}
+
 /***********************************************************
  * DESCRIPTION:
  * select_handler constructor
  * PARAMETERS:
  *    thd - THD pointer.
- *    select_lex - sematic tree for the query.
+ *    sel_lex - semantic tree for the query.
  ***********************************************************/
-ha_columnstore_select_handler::ha_columnstore_select_handler(THD* thd, SELECT_LEX* select_lex)
+ha_columnstore_select_handler::ha_columnstore_select_handler(THD* thd, SELECT_LEX* sel_lex)
- : select_handler(thd, mcs_hton)
+ : select_handler(thd, mcs_hton, sel_lex)
+ , prepared(false)
+ , scan_ended(false)
+ , scan_initialized(false)
+ , pushdown_init_rc(0)
+{
+  const char* timeZone = thd->variables.time_zone->get_name()->ptr();
+  dataconvert::timeZoneToOffset(timeZone, strlen(timeZone), &time_zone);
+}
+
+/***********************************************************
+ * DESCRIPTION:
+ * select_handler constructor
+ * PARAMETERS:
+ *    thd - THD pointer.
+ *    sel_unit - semantic tree for the query.
+ ***********************************************************/
+ha_columnstore_select_handler::ha_columnstore_select_handler(THD* thd, SELECT_LEX_UNIT* sel_unit)
+ : select_handler(thd, mcs_hton, sel_unit)
+ , prepared(false)
+ , scan_ended(false)
+ , scan_initialized(false)
+ , pushdown_init_rc(0)
+{
+  const char* timeZone = thd->variables.time_zone->get_name()->ptr();
+  dataconvert::timeZoneToOffset(timeZone, strlen(timeZone), &time_zone);
+}
+
+/***********************************************************
+ * DESCRIPTION:
+ * select_handler constructor
+ * PARAMETERS:
+ *    thd - THD pointer.
+ *    sel_lex - semantic tree for the query.
+ *    sel_unit - unit containing SELECT_LEX's
+ ***********************************************************/
+ha_columnstore_select_handler::ha_columnstore_select_handler(THD* thd, SELECT_LEX* sel_lex,
+                                                             SELECT_LEX_UNIT* sel_unit)
+ : select_handler(thd, mcs_hton, sel_lex, sel_unit)
  , prepared(false)
  , scan_ended(false)
  , scan_initialized(false)
  , pushdown_init_rc(0)
 {
-  select = select_lex;
   const char* timeZone = thd->variables.time_zone->get_name()->ptr();
   dataconvert::timeZoneToOffset(timeZone, strlen(timeZone), &time_zone);
 }
@@ -1074,7 +1173,7 @@ bool ha_columnstore_select_handler::prepare()
 
   prepared = true;
 
-  if ((!table && !(table = create_tmp_table(thd, select))) || table->fill_item_list(&result_columns))
+  if ((!table && !(table = create_tmp_table(thd))) || table->fill_item_list(&result_columns))
   {
     pushdown_init_rc = 1;
     DBUG_RETURN(true);

dbcon/mysql/ha_mcs_pushdown.h

@@ -151,7 +151,9 @@ class ha_columnstore_select_handler : public select_handler
   // This will be used to restore to the original state later in case
   // query execution fails using the select_handler.
   cal_impl_if::TableOuterJoinMap tableOuterJoinMap;
-  ha_columnstore_select_handler(THD* thd_arg, SELECT_LEX* sel);
+  ha_columnstore_select_handler(THD* thd_arg, SELECT_LEX* sel_lex);
+  ha_columnstore_select_handler(THD* thd_arg, SELECT_LEX_UNIT* sel_unit);
+  ha_columnstore_select_handler(THD* thd_arg, SELECT_LEX* sel_lex, SELECT_LEX_UNIT* sel_unit);
   ~ha_columnstore_select_handler();
   int init_scan() override;
   int next_row() override;

mysql-test/columnstore/basic/r/mdev-25080.result

@@ -0,0 +1,114 @@
+#
+# MDEV-25080: Allow pushdown of queries involving UNIONs
+# in outer select to foreign engines
+#
+# Uncomment the actual SELECTs and add ORDER BY clause
+# after MCOL-5222 is fixed
+#
+CREATE USER IF NOT EXISTS'cejuser'@'localhost' IDENTIFIED BY 'Vagrant1|0000001';
+GRANT ALL PRIVILEGES ON *.* TO 'cejuser'@'localhost';
+FLUSH PRIVILEGES;
+DROP DATABASE IF EXISTS mdev25080;
+CREATE DATABASE mdev25080;
+USE mdev25080;
+CREATE TABLE t1 (a varchar(30)) ENGINE=ColumnStore;
+CREATE TABLE t2 (a varchar(30)) ENGINE=ColumnStore;
+CREATE TABLE t3 (a varchar(30)) ENGINE=MyISAM;
+CREATE TABLE t4 (a varchar(30)) ENGINE=MyISAM;
+INSERT INTO t1 VALUES ('abc'), ('bcd'), ('cde');
+INSERT INTO t2 VALUES ('bcd'), ('cde'), ('def'), ('efg');
+INSERT INTO t3 VALUES ('t3_myisam1'), ('t3_myisam2'), ('t3_myisam3');
+INSERT INTO t4 VALUES ('t4_myisam1'), ('t4_myisam2'), ('t4_myisam3');
+# Pushdown of the whole UNION
+EXPLAIN SELECT * FROM t1 UNION SELECT * FROM t2;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+NULL	PUSHED UNION	NULL	NULL	NULL	NULL	NULL	NULL	NULL	NULL
+EXPLAIN SELECT * FROM t1 UNION ALL SELECT * FROM t2;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+NULL	PUSHED UNION	NULL	NULL	NULL	NULL	NULL	NULL	NULL	NULL
+# UNION with a foreign engine
+EXPLAIN SELECT * FROM t1 UNION SELECT * FROM t3;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+NULL	PUSHED UNION	NULL	NULL	NULL	NULL	NULL	NULL	NULL	NULL
+# More than two SELECTs in a UNIT:
+EXPLAIN SELECT * FROM t1 UNION
+SELECT * FROM t2 UNION ALL
+SELECT * FROM t1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+NULL	PUSHED UNION	NULL	NULL	NULL	NULL	NULL	NULL	NULL	NULL
+EXPLAIN (SELECT * FROM t1 UNION
+SELECT * FROM t2) UNION ALL
+SELECT * FROM t1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+NULL	PUSHED UNION	NULL	NULL	NULL	NULL	NULL	NULL	NULL	NULL
+EXPLAIN SELECT * FROM t1 UNION
+SELECT * FROM t2 UNION ALL
+SELECT * FROM t3 UNION
+SELECT * FROM t4;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+NULL	PUSHED UNION	NULL	NULL	NULL	NULL	NULL	NULL	NULL	NULL
+EXPLAIN (SELECT * FROM t1 UNION
+SELECT * FROM t2) UNION ALL
+(SELECT * FROM t3 UNION
+SELECT * FROM t4);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+NULL	PUSHED UNION	NULL	NULL	NULL	NULL	NULL	NULL	NULL	NULL
+EXPLAIN
+SELECT count(*) FROM t1 UNION
+SELECT count(*) FROM t2 UNION ALL
+SELECT count(*)+20 FROM t2 UNION
+SELECT count(*)+5 FROM t1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+NULL	PUSHED UNION	NULL	NULL	NULL	NULL	NULL	NULL	NULL	NULL
+# UNION inside a derived table: the whole derived table must be pushed
+SELECT a FROM
+(SELECT a FROM t1 UNION ALL SELECT a FROM t2) q ORDER BY a;
+a
+abc
+bcd
+bcd
+cde
+cde
+def
+efg
+EXPLAIN
+SELECT a FROM
+(SELECT a FROM t1 UNION ALL SELECT a FROM t2) q ORDER BY a;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PUSHED SELECT	NULL	NULL	NULL	NULL	NULL	NULL	NULL	NULL
+SELECT a FROM
+(SELECT a FROM t1 UNION ALL SELECT a FROM t3) q ORDER BY a;
+a
+abc
+bcd
+cde
+t3_myisam1
+t3_myisam2
+t3_myisam3
+EXPLAIN
+SELECT a FROM
+(SELECT a FROM t1 UNION ALL SELECT a FROM t3) q ORDER BY a;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PUSHED SELECT	NULL	NULL	NULL	NULL	NULL	NULL	NULL	NULL
+# Prepared statements
+PREPARE stmt FROM "EXPLAIN SELECT * FROM t1 UNION
+  SELECT * FROM t2";
+EXECUTE stmt;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+NULL	PUSHED UNION	NULL	NULL	NULL	NULL	NULL	NULL	NULL	NULL
+EXECUTE stmt;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+NULL	PUSHED UNION	NULL	NULL	NULL	NULL	NULL	NULL	NULL	NULL
+PREPARE stmt FROM "EXPLAIN (SELECT * FROM t1 UNION
+  SELECT * FROM t2) UNION ALL
+  (SELECT * FROM t1 UNION
+  SELECT * FROM t2)";
+EXECUTE stmt;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+NULL	PUSHED UNION	NULL	NULL	NULL	NULL	NULL	NULL	NULL	NULL
+EXECUTE stmt;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+NULL	PUSHED UNION	NULL	NULL	NULL	NULL	NULL	NULL	NULL	NULL
+DROP USER 'cejuser'@'localhost';
+DROP TABLE t1, t2, t3, t4;
+DROP DATABASE mdev25080;

mysql-test/columnstore/basic/r/union.result

@@ -5,6 +5,9 @@ USE mcs_union;
 #
 # MCOL-4700 Wrong result of a UNION for INT and INT UNSIGNED
 #
+# Move the UNIONs from the subqueries to outer selects and add
+# ORDER BY clause after MCOL-5222 is fixed
+#
 CREATE TABLE t1 (a INT, b INT UNSIGNED);
 INSERT INTO t1 VALUES (-1, 1), (-1, 1), (-2, 2);
 SELECT * FROM (SELECT * FROM t1 UNION SELECT * FROM t1) tu ORDER BY b;
@@ -862,4 +865,27 @@ a
 16777213
 9223372036854775807
 DROP TABLE t1,t2;
+#
+# Union of tables containing different string data types
+#
+# Uncomment the actual SELECTs and add ORDER BY clause
+# after MCOL-5222 is fixed
+#
+CREATE TABLE t1 (a CHAR(6));
+INSERT INTO t1 VALUES ('t13abc'), ('t13xx'), ('common');
+CREATE TABLE t2 (a VARCHAR(8));
+INSERT INTO t2 VALUES ('t14abcde'), ('t14xyzzz'), ('common');
+EXPLAIN SELECT * FROM t1 UNION SELECT * FROM t2;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+NULL	PUSHED UNION	NULL	NULL	NULL	NULL	NULL	NULL	NULL	NULL
+EXPLAIN SELECT * FROM t2 UNION ALL SELECT * FROM t1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+NULL	PUSHED UNION	NULL	NULL	NULL	NULL	NULL	NULL	NULL	NULL
+EXPLAIN SELECT * FROM t1 UNION SELECT * FROM t2 UNION SELECT '123456789000';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+NULL	PUSHED UNION	NULL	NULL	NULL	NULL	NULL	NULL	NULL	NULL
+EXPLAIN SELECT * FROM t1 UNION SELECT '123456789000' UNION SELECT * FROM t2;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+NULL	PUSHED UNION	NULL	NULL	NULL	NULL	NULL	NULL	NULL	NULL
+DROP TABLE t1,t2;
 DROP DATABASE mcs_union;

mysql-test/columnstore/basic/t/mdev-25080.test

@@ -0,0 +1,154 @@
+--echo #
+--echo # MDEV-25080: Allow pushdown of queries involving UNIONs
+--echo # in outer select to foreign engines
+--echo #
+--echo # Uncomment the actual SELECTs and add ORDER BY clause
+--echo # after MCOL-5222 is fixed
+--echo #
+
+--source ../include/have_columnstore.inc
+
+#
+# Enable cross engine join
+# Configure user and password in Columnstore.xml file
+#
+--exec $MCS_MCSSETCONFIG CrossEngineSupport User 'cejuser'
+--exec $MCS_MCSSETCONFIG CrossEngineSupport Password 'Vagrant1|0000001'
+--exec $MCS_MCSSETCONFIG CrossEngineSupport Port $MASTER_MYPORT
+
+#
+# Create corresponding in the server
+#
+--disable_warnings
+CREATE USER IF NOT EXISTS'cejuser'@'localhost' IDENTIFIED BY 'Vagrant1|0000001';
+--enable_warnings
+GRANT ALL PRIVILEGES ON *.* TO 'cejuser'@'localhost';
+FLUSH PRIVILEGES;
+
+--disable_warnings
+DROP DATABASE IF EXISTS mdev25080;
+--enable_warnings
+
+CREATE DATABASE mdev25080;
+
+USE mdev25080;
+
+CREATE TABLE t1 (a varchar(30)) ENGINE=ColumnStore;
+CREATE TABLE t2 (a varchar(30)) ENGINE=ColumnStore;
+CREATE TABLE t3 (a varchar(30)) ENGINE=MyISAM;
+CREATE TABLE t4 (a varchar(30)) ENGINE=MyISAM;
+
+INSERT INTO t1 VALUES ('abc'), ('bcd'), ('cde');
+INSERT INTO t2 VALUES ('bcd'), ('cde'), ('def'), ('efg');
+
+INSERT INTO t3 VALUES ('t3_myisam1'), ('t3_myisam2'), ('t3_myisam3');
+INSERT INTO t4 VALUES ('t4_myisam1'), ('t4_myisam2'), ('t4_myisam3');
+
+--echo # Pushdown of the whole UNION
+#SELECT * FROM t1 UNION SELECT * FROM t2;
+EXPLAIN SELECT * FROM t1 UNION SELECT * FROM t2;
+
+#SELECT * FROM t1 UNION ALL SELECT * FROM t2;
+EXPLAIN SELECT * FROM t1 UNION ALL SELECT * FROM t2;
+
+--echo # UNION with a foreign engine
+#SELECT * FROM t1 UNION SELECT * FROM t3;
+EXPLAIN SELECT * FROM t1 UNION SELECT * FROM t3;
+
+--echo # More than two SELECTs in a UNIT:
+#SELECT * FROM t1 UNION
+#  SELECT * FROM t2 UNION ALL
+#  SELECT * FROM t1;
+
+EXPLAIN SELECT * FROM t1 UNION
+  SELECT * FROM t2 UNION ALL
+  SELECT * FROM t1;
+
+#(SELECT * FROM t1 UNION
+#  SELECT * FROM t2) UNION ALL
+#  SELECT * FROM t1;
+
+EXPLAIN (SELECT * FROM t1 UNION
+  SELECT * FROM t2) UNION ALL
+  SELECT * FROM t1;
+
+#SELECT * FROM t1 UNION
+#  SELECT * FROM t2 UNION ALL
+#  SELECT * FROM t3 UNION
+#  SELECT * FROM t4;
+
+EXPLAIN SELECT * FROM t1 UNION
+  SELECT * FROM t2 UNION ALL
+  SELECT * FROM t3 UNION
+  SELECT * FROM t4;
+
+#(SELECT * FROM t1 UNION
+#  SELECT * FROM t2) UNION ALL
+#  (SELECT * FROM t3 UNION
+#  SELECT * FROM t4);
+
+EXPLAIN (SELECT * FROM t1 UNION
+  SELECT * FROM t2) UNION ALL
+  (SELECT * FROM t3 UNION
+  SELECT * FROM t4);
+
+#SELECT count(*) FROM t1 UNION
+#  SELECT count(*) FROM t2 UNION ALL
+#  SELECT count(*)+20 FROM t2 UNION
+#  SELECT count(*)+5 FROM t1;
+
+EXPLAIN
+  SELECT count(*) FROM t1 UNION
+  SELECT count(*) FROM t2 UNION ALL
+  SELECT count(*)+20 FROM t2 UNION
+  SELECT count(*)+5 FROM t1;
+
+--echo # UNION inside a derived table: the whole derived table must be pushed
+SELECT a FROM
+  (SELECT a FROM t1 UNION ALL SELECT a FROM t2) q ORDER BY a;
+
+EXPLAIN
+  SELECT a FROM
+    (SELECT a FROM t1 UNION ALL SELECT a FROM t2) q ORDER BY a;
+
+SELECT a FROM
+  (SELECT a FROM t1 UNION ALL SELECT a FROM t3) q ORDER BY a;
+
+EXPLAIN
+  SELECT a FROM
+    (SELECT a FROM t1 UNION ALL SELECT a FROM t3) q ORDER BY a;
+
+--echo # Prepared statements
+#PREPARE stmt FROM "SELECT * FROM t1 UNION
+#  SELECT * FROM t2";
+
+#EXECUTE stmt;
+#EXECUTE stmt;
+#EXECUTE stmt;
+
+PREPARE stmt FROM "EXPLAIN SELECT * FROM t1 UNION
+  SELECT * FROM t2";
+
+EXECUTE stmt;
+EXECUTE stmt;
+
+#PREPARE stmt FROM "(SELECT * FROM t1 UNION
+#  SELECT * FROM t2) UNION ALL
+#  (SELECT * FROM t1 UNION
+#  SELECT * FROM t2)";
+
+#EXECUTE stmt;
+#EXECUTE stmt;
+#EXECUTE stmt;
+
+PREPARE stmt FROM "EXPLAIN (SELECT * FROM t1 UNION
+  SELECT * FROM t2) UNION ALL
+  (SELECT * FROM t1 UNION
+  SELECT * FROM t2)";
+
+EXECUTE stmt;
+EXECUTE stmt;
+
+DROP USER 'cejuser'@'localhost';
+DROP TABLE t1, t2, t3, t4;
+DROP DATABASE mdev25080;

mysql-test/columnstore/basic/t/union.test

@@ -12,6 +12,9 @@ USE mcs_union;
 --echo #
 --echo # MCOL-4700 Wrong result of a UNION for INT and INT UNSIGNED
 --echo #
+--echo # Move the UNIONs from the subqueries to outer selects and add
+--echo # ORDER BY clause after MCOL-5222 is fixed
+--echo #
 
 CREATE TABLE t1 (a INT, b INT UNSIGNED);
 INSERT INTO t1 VALUES (-1, 1), (-1, 1), (-2, 2);
@@ -273,4 +276,25 @@ SELECT * FROM (SELECT a FROM t1 UNION ALL SELECT a FROM t2) tu ORDER BY a;
 SELECT * FROM (SELECT a FROM t2 UNION ALL SELECT a FROM t1) tu ORDER BY a;
 DROP TABLE t1,t2;
 
+--echo #
+--echo # Union of tables containing different string data types
+--echo #
+--echo # Uncomment the actual SELECTs and add ORDER BY clause
+--echo # after MCOL-5222 is fixed
+--echo #
+
+CREATE TABLE t1 (a CHAR(6));
+INSERT INTO t1 VALUES ('t13abc'), ('t13xx'), ('common');
+CREATE TABLE t2 (a VARCHAR(8));
+INSERT INTO t2 VALUES ('t14abcde'), ('t14xyzzz'), ('common');
+#SELECT * FROM t1 UNION SELECT * FROM t2;
+EXPLAIN SELECT * FROM t1 UNION SELECT * FROM t2;
+#SELECT * FROM t2 UNION ALL SELECT * FROM t1;
+EXPLAIN SELECT * FROM t2 UNION ALL SELECT * FROM t1;
+#SELECT * FROM t1 UNION SELECT * FROM t2 UNION SELECT '123456789000';
+EXPLAIN SELECT * FROM t1 UNION SELECT * FROM t2 UNION SELECT '123456789000';
+#SELECT * FROM t1 UNION SELECT '123456789000' UNION SELECT * FROM t2;
+EXPLAIN SELECT * FROM t1 UNION SELECT '123456789000' UNION SELECT * FROM t2;
+DROP TABLE t1,t2;
+
 DROP DATABASE mcs_union;