MDEV-30828 Prevent pushing down unions with incorrect ORDER BY

Fake_select_lex->join was prepared at the unit execution stage so the validation of fake_select_lex before the unit pushdown was incomplete. That caused pushing down of statements having an incorrect ORDER BY clause. This commit moves preparation of the fake_select_lex->join to the unit prepare() method, before initializing of the pushdown handler, so incorrect clauses error out before being pushed down
2025-07-30 16:24:05 +03:00 · 2023-04-03 18:05:44 +07:00
parent 8290a46d50
commit d6c6102cad
7 changed files with 238 additions and 148 deletions
--- a/mysql-test/main/opt_trace.result
+++ b/mysql-test/main/opt_trace.result
@ -11720,6 +11720,16 @@ UPDATE t, v SET t.b = t.a, t.a = v.c WHERE v.c < t.a	{
        ]
      }
    },
+    {
+      "join_preparation": {
+        "select_id": "fake",
+        "steps": [
+          {
+            "expanded_query": "select c AS c from dual"
+          }
+        ]
+      }
+    },
    {
      "join_preparation": {
        "select_id": 1,
@ -11967,16 +11977,6 @@ UPDATE t, v SET t.b = t.a, t.a = v.c WHERE v.c < t.a	{
              "steps": []
            }
          },
-          {
-            "join_preparation": {
-              "select_id": "fake",
-              "steps": [
-                {
-                  "expanded_query": "select c AS c from dual"
-                }
-              ]
-            }
-          },
          {
            "join_optimization": {
              "select_id": "fake",
--- a/mysql-test/suite/federated/federatedx_create_handlers.result
+++ b/mysql-test/suite/federated/federatedx_create_handlers.result
@ -572,8 +572,8 @@ CREATE TABLE federated.t2 (
 a varchar(16) NOT NULL default ''
 )
 DEFAULT CHARSET=latin1;
-INSERT INTO federated.t1 VALUES ('abc'), ('bcd'), ('cde');
-INSERT INTO federated.t2 VALUES ('abc'), ('bcd'), ('cde'), ('def'), ('efg');
+INSERT INTO federated.t1 VALUES ('bcd'), ('abc'), ('cde');
+INSERT INTO federated.t2 VALUES ('cde'), ('efg'), ('abc'), ('bcd'), ('def');
 connection master;
 CREATE TABLE federated.t1 (
 a varchar(10)
@ -617,10 +617,10 @@ NULL	UNION RESULT	<union1,2>	ALL	NULL	NULL	NULL	NULL	NULL
 SELECT * from federated.t1 UNION ALL SELECT * from federated.t2;
 a
 abc
-bcd
-cde
 abc
 bcd
+bcd
+cde
 cde
 def
 efg
@ -730,10 +730,10 @@ SELECT * FROM
 (SELECT * FROM federated.t1 UNION ALL SELECT * FROM federated.t2) q;
 a
 abc
-bcd
-cde
 abc
 bcd
+bcd
+cde
 cde
 def
 efg
@ -861,12 +861,12 @@ SELECT * FROM federated.t1 EXCEPT
 SELECT * FROM t4 INTERSECT
 SELECT * FROM federated.t2;
 a
-t3_myisam1
-t3_myisam2
-t3_myisam3
 abc
 bcd
 cde
+t3_myisam1
+t3_myisam2
+t3_myisam3
 EXPLAIN SELECT * FROM t3 UNION ALL
 SELECT * FROM federated.t1 EXCEPT
 SELECT * FROM t4 INTERSECT
@ -915,13 +915,13 @@ SELECT * FROM federated.t2) UNION ALL
 SELECT * FROM federated.t1;
 a
 abc
+abc
 bcd
+bcd
+cde
 cde
 def
 efg
-abc
-bcd
-cde
 EXPLAIN (SELECT * FROM federated.t1 UNION SELECT * FROM federated.t2)
 UNION ALL (SELECT * FROM federated.t1 UNION SELECT * FROM federated.t2);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
@ -930,14 +930,14 @@ NULL	PUSHED UNION	NULL	NULL	NULL	NULL	NULL	NULL	NULL	NULL
 (SELECT * FROM federated.t1 UNION SELECT * FROM federated.t2);
 a
 abc
-bcd
-cde
-def
-efg
 abc
 bcd
+bcd
+cde
 cde
 def
+def
+efg
 efg
 # Union of tables containing different INT data types
 connection slave;
@ -955,31 +955,31 @@ CONNECTION='mysql://root@127.0.0.1:SLAVE_PORT/federated/t12';
 # Entire UNION pushdown
 SELECT a FROM federated.t12 UNION ALL SELECT a FROM federated.t11;
 a
+-1
+-32678
+0
 0
 1
 32767
-32678
-1
-0
 EXPLAIN SELECT a FROM federated.t12 UNION ALL SELECT a FROM federated.t11;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 NULL	PUSHED UNION	NULL	NULL	NULL	NULL	NULL	NULL	NULL	NULL
 SELECT a FROM federated.t11 UNION SELECT a FROM federated.t12;
 a
-32678
 -1
+-32678
 0
 1
 32767
 # Partial pushdown of SELECTs composing the UNION
 SELECT a FROM federated.t12 UNION SELECT a FROM federated.t11 UNION SELECT 123;
 a
+-1
+-32678
 0
 1
-32767
-32678
-1
 123
+32767
 EXPLAIN
 SELECT a FROM federated.t12 UNION SELECT a FROM federated.t11
 UNION SELECT 123;
@ -993,9 +993,9 @@ SELECT 1 UNION ALL
 SELECT a FROM federated.t11 EXCEPT
 SELECT 0;
 a
+-1
 -32678
 32767
-1
 # Union of tables containing different string data types
 connection slave;
 CREATE TABLE federated.t13 (a CHAR(6));
@ -1011,9 +1011,9 @@ ENGINE="FEDERATED"
 CONNECTION='mysql://root@127.0.0.1:SLAVE_PORT/federated/t14';
 SELECT * FROM federated.t13 UNION SELECT * FROM federated.t14;
 a
+common
 t13abc
 t13xx
-common
 t14abcde
 t14xyzzz
 EXPLAIN SELECT * FROM federated.t13 UNION SELECT * FROM federated.t14;
@ -1021,12 +1021,12 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 NULL	PUSHED UNION	NULL	NULL	NULL	NULL	NULL	NULL	NULL	NULL
 SELECT * FROM federated.t14 UNION ALL SELECT * FROM federated.t13;
 a
-t14abcde
-t14xyzzz
+common
 common
 t13abc
 t13xx
-common
+t14abcde
+t14xyzzz
 SELECT * FROM federated.t14 UNION
 SELECT * FROM federated.t13 UNION
 SELECT '123456789000';
@ -1049,10 +1049,10 @@ SELECT * FROM federated.t13 UNION
 SELECT '123456789000' UNION
 SELECT * FROM federated.t14;
 a
+123456789000
+common
 t13abc
 t13xx
-common
-123456789000
 t14abcde
 t14xyzzz
 # CREATE TABLE .. AS from a pushed UNION
@ -1084,6 +1084,61 @@ a
 -1
 -32678
 32767
+#
+# MDEV-30828 ORDER BY clause using an integer (positional argument)
+#
+SELECT a FROM federated.t1 UNION SELECT a FROM federated.t2 ORDER BY 1;
+a
+abc
+bcd
+cde
+def
+efg
+SELECT a FROM federated.t1 UNION ALL SELECT a FROM federated.t2 ORDER BY a DESC;
+a
+efg
+def
+cde
+cde
+bcd
+bcd
+abc
+abc
+# Check handling of incorrect ORDER BY clause
+SELECT a FROM federated.t1 UNION SELECT a FROM federated.t2 ORDER BY 2;
+ERROR 42S22: Unknown column '2' in 'order clause'
+PREPARE stmt FROM
+"SELECT a FROM federated.t1 UNION ALL SELECT a FROM federated.t2 ORDER BY 2";
+ERROR 42S22: Unknown column '2' in 'order clause'
+SELECT a FROM federated.t1 UNION ALL SELECT a FROM federated.t2 ORDER BY 2,1,3;
+ERROR 42S22: Unknown column '2' in 'order clause'
+SELECT a FROM federated.t1 UNION ALL SELECT a FROM federated.t2 ORDER BY t1.a;
+ERROR 42000: Table 't1' from one of the SELECTs cannot be used in ORDER clause
+SELECT * from federated.t1 INTERSECT
+SELECT * from federated.t2 UNION ALL
+SELECT * from federated.t2 EXCEPT
+SELECT * from federated.t1
+ORDER BY 1;
+a
+def
+efg
+SELECT * from federated.t1 INTERSECT
+SELECT * from federated.t2 UNION ALL
+SELECT * from federated.t2 EXCEPT
+SELECT * from federated.t1
+ORDER BY 3;
+ERROR 42S22: Unknown column '3' in 'order clause'
+# UNION of mixed Federated/MyISAM tables, pushing parts of UNIONs
+SELECT * FROM federated.t1 UNION SELECT * FROM t3 ORDER BY a;
+a
+abc
+bcd
+cde
+t3_myisam1
+t3_myisam2
+t3_myisam3
+SELECT * FROM federated.t1 UNION SELECT * FROM t3 ORDER BY 2;
+ERROR 42S22: Unknown column '2' in 'order clause'
 connection master;
 DROP TABLES federated.t1, federated.t2, t3, t4, t5, t6, federated.t11,
 federated.t12, federated.t13, federated.t14;
--- a/mysql-test/suite/federated/federatedx_create_handlers.test
+++ b/mysql-test/suite/federated/federatedx_create_handlers.test
@ -398,8 +398,8 @@ CREATE TABLE federated.t2 (
 )
 DEFAULT CHARSET=latin1;

-INSERT INTO federated.t1 VALUES ('abc'), ('bcd'), ('cde');
-INSERT INTO federated.t2 VALUES ('abc'), ('bcd'), ('cde'), ('def'), ('efg');
+INSERT INTO federated.t1 VALUES ('bcd'), ('abc'), ('cde');
+INSERT INTO federated.t2 VALUES ('cde'), ('efg'), ('abc'), ('bcd'), ('def');

 connection master;

@ -426,13 +426,16 @@ 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
+--sorted_result
 SELECT * from federated.t1 UNION SELECT * from federated.t2;
 EXPLAIN SELECT * from federated.t1 UNION SELECT * from federated.t2;

 --echo # Pushdown of a part of the UNION
+--sorted_result
 SELECT * from federated.t1 UNION SELECT * from t3;
 EXPLAIN SELECT * from federated.t1 UNION SELECT * from t3;

+--sorted_result
 SELECT * from federated.t1 UNION ALL SELECT * from federated.t2;
 EXPLAIN SELECT * from federated.t1 UNION ALL SELECT * from federated.t2;

@ -445,6 +448,7 @@ ANALYZE SELECT * from federated.t1 UNION ALL SELECT * from federated.t2;
 ANALYZE FORMAT=JSON SELECT * from federated.t1 UNION ALL
  SELECT * from federated.t2;

+--sorted_result
 SELECT * from federated.t1 EXCEPT SELECT * from federated.t2;

 EXPLAIN EXTENDED SELECT * from federated.t1 EXCEPT
@ -453,6 +457,7 @@ EXPLAIN EXTENDED SELECT * from federated.t1 EXCEPT
 EXPLAIN FORMAT=JSON SELECT * from federated.t1 EXCEPT
  SELECT * from federated.t2;

+--sorted_result
 SELECT * from federated.t1 INTERSECT SELECT * from federated.t2;

 EXPLAIN PARTITIONS SELECT * from federated.t1 INTERSECT
@ -462,6 +467,7 @@ EXPLAIN FORMAT=JSON SELECT * from federated.t1 INTERSECT
  SELECT * from federated.t2;

 --echo # More than two SELECTs in a UNIT:
+--sorted_result
 SELECT * from federated.t1 INTERSECT
  SELECT * from federated.t2 UNION ALL
  SELECT * from federated.t2 EXCEPT
@ -486,6 +492,7 @@ ANALYZE
  SELECT count(*)+5 from federated.t1;

 --echo # UNION inside a derived table: the whole derived table must be pushed
+--sorted_result
 SELECT * FROM 
  (SELECT * FROM federated.t1 UNION ALL SELECT * FROM federated.t2) q;

@ -499,6 +506,7 @@ EXPLAIN
 --echo # at the server side

 --disable_warnings
+--sorted_result
 SELECT count(*) FROM federated.t1 UNION
  SELECT count(*) FROM federated.t1 EXCEPT
  SELECT count(*)+1 FROM federated.t1
@ -521,8 +529,11 @@ PREPARE stmt FROM "SELECT * from federated.t1 INTERSECT
  SELECT * from federated.t2 EXCEPT
  SELECT * from federated.t1";

+--sorted_result
 EXECUTE stmt;
+--sorted_result
 EXECUTE stmt;
+--sorted_result
 EXECUTE stmt;

 PREPARE stmt FROM "EXPLAIN SELECT * from federated.t1 INTERSECT
@ -530,13 +541,17 @@ PREPARE stmt FROM "EXPLAIN SELECT * from federated.t1 INTERSECT
  SELECT * from federated.t2 EXCEPT
  SELECT * from federated.t1";

+--sorted_result
 EXECUTE stmt;
+--sorted_result
 EXECUTE stmt;

 --echo # UNIONs of mixed Federated/MyISAM tables, pushing parts of UNIONs
+--sorted_result
 SELECT * FROM federated.t1 UNION SELECT * FROM t3;
 EXPLAIN SELECT * FROM federated.t1 UNION SELECT * FROM t3;

+--sorted_result
 SELECT * FROM federated.t1 UNION ALL
  SELECT * FROM t3 EXCEPT
  SELECT * FROM federated.t2;
@ -544,6 +559,7 @@ EXPLAIN SELECT * FROM federated.t1 UNION ALL
  SELECT * FROM t3 EXCEPT
  SELECT * FROM federated.t2;

+--sorted_result
 SELECT * FROM t3 UNION ALL
  SELECT * FROM federated.t1 EXCEPT
  SELECT * FROM t4 INTERSECT
@ -553,6 +569,7 @@ EXPLAIN SELECT * FROM t3 UNION ALL
  SELECT * FROM t4 INTERSECT
  SELECT * FROM federated.t2;

+--sorted_result
 SELECT * FROM federated.t2 UNION ALL
  SELECT * FROM t3 EXCEPT
  SELECT * FROM t4 INTERSECT
@ -567,6 +584,7 @@ EXPLAIN (SELECT * FROM federated.t1 UNION
  SELECT * FROM federated.t2) UNION ALL
  SELECT * FROM federated.t1;

+--sorted_result
 (SELECT * FROM federated.t1 UNION
  SELECT * FROM federated.t2) UNION ALL
  SELECT * FROM federated.t1;
@ -574,6 +592,7 @@ EXPLAIN (SELECT * FROM federated.t1 UNION
 EXPLAIN (SELECT * FROM federated.t1 UNION SELECT * FROM federated.t2)
  UNION ALL (SELECT * FROM federated.t1 UNION SELECT * FROM federated.t2);

+--sorted_result
 (SELECT * FROM federated.t1 UNION SELECT * FROM federated.t2) UNION ALL
  (SELECT * FROM federated.t1 UNION SELECT * FROM federated.t2);
  
@ -601,17 +620,21 @@ ENGINE="FEDERATED"
 CONNECTION='mysql://root@127.0.0.1:$SLAVE_MYPORT/federated/t12';

 --echo # Entire UNION pushdown
+--sorted_result
 SELECT a FROM federated.t12 UNION ALL SELECT a FROM federated.t11;
 EXPLAIN SELECT a FROM federated.t12 UNION ALL SELECT a FROM federated.t11;

+--sorted_result
 SELECT a FROM federated.t11 UNION SELECT a FROM federated.t12;

 --echo # Partial pushdown of SELECTs composing the UNION
+--sorted_result
 SELECT a FROM federated.t12 UNION SELECT a FROM federated.t11 UNION SELECT 123;
 EXPLAIN
  SELECT a FROM federated.t12 UNION SELECT a FROM federated.t11
  UNION SELECT 123;

+--sorted_result
 SELECT a FROM federated.t12 EXCEPT
  SELECT 1 UNION ALL
  SELECT a FROM federated.t11 EXCEPT
@ -639,9 +662,11 @@ CREATE TABLE federated.t14 (a VARCHAR(8))
 ENGINE="FEDERATED"
 CONNECTION='mysql://root@127.0.0.1:$SLAVE_MYPORT/federated/t14';

+--sorted_result
 SELECT * FROM federated.t13 UNION SELECT * FROM federated.t14;
 EXPLAIN SELECT * FROM federated.t13 UNION SELECT * FROM federated.t14;

+--sorted_result
 SELECT * FROM federated.t14 UNION ALL SELECT * FROM federated.t13;

 SELECT * FROM federated.t14 UNION
@ -652,6 +677,7 @@ EXPLAIN SELECT * FROM federated.t14 UNION
  SELECT * FROM federated.t13 UNION
  SELECT '123456789000';

+--sorted_result
 SELECT * FROM federated.t13 UNION
  SELECT '123456789000' UNION
  SELECT * FROM federated.t14;
@ -671,6 +697,41 @@ SHOW CREATE TABLE t6;
 --sorted_result
 SELECT * FROM t6;

+--echo #
+--echo # MDEV-30828 ORDER BY clause using an integer (positional argument)
+--echo #
+SELECT a FROM federated.t1 UNION SELECT a FROM federated.t2 ORDER BY 1;
+
+SELECT a FROM federated.t1 UNION ALL SELECT a FROM federated.t2 ORDER BY a DESC;
+
+--echo # Check handling of incorrect ORDER BY clause
+--error ER_BAD_FIELD_ERROR
+SELECT a FROM federated.t1 UNION SELECT a FROM federated.t2 ORDER BY 2;
+--error ER_BAD_FIELD_ERROR
+PREPARE stmt FROM
+  "SELECT a FROM federated.t1 UNION ALL SELECT a FROM federated.t2 ORDER BY 2";
+
+--error ER_BAD_FIELD_ERROR
+SELECT a FROM federated.t1 UNION ALL SELECT a FROM federated.t2 ORDER BY 2,1,3;
+--error ER_TABLENAME_NOT_ALLOWED_HERE
+SELECT a FROM federated.t1 UNION ALL SELECT a FROM federated.t2 ORDER BY t1.a;
+SELECT * from federated.t1 INTERSECT
+  SELECT * from federated.t2 UNION ALL
+  SELECT * from federated.t2 EXCEPT
+  SELECT * from federated.t1
+  ORDER BY 1;
+--error ER_BAD_FIELD_ERROR
+SELECT * from federated.t1 INTERSECT
+  SELECT * from federated.t2 UNION ALL
+  SELECT * from federated.t2 EXCEPT
+  SELECT * from federated.t1
+  ORDER BY 3;
+--echo # UNION of mixed Federated/MyISAM tables, pushing parts of UNIONs
+SELECT * FROM federated.t1 UNION SELECT * FROM t3 ORDER BY a;
+--error ER_BAD_FIELD_ERROR
+SELECT * FROM federated.t1 UNION SELECT * FROM t3 ORDER BY 2;
+
+
 # Cleanup
 connection master;
 DROP TABLES federated.t1, federated.t2, t3, t4, t5, t6, federated.t11,
--- a/sql/sql_lex.h
+++ b/sql/sql_lex.h
@ -1057,6 +1057,8 @@ private:
  bool exec_inner();
  bool is_derived_eliminated() const;
  bool set_direct_union_result(select_result *sel_result);
+  bool prepare_pushdown(bool use_direct_union_result,
+                        select_result *sel_result);
 };

 typedef class st_select_lex_unit SELECT_LEX_UNIT;
--- a/sql/sql_select.cc
+++ b/sql/sql_select.cc
@ -563,6 +563,7 @@ void JOIN::init(THD *thd_arg, List<Item> &fields_arg,
  sjm_scan_tables= 0;
  is_orig_degenerated= false;
  with_ties_order_count= 0;
+  prepared= false;
 };


@ -1816,6 +1817,7 @@ JOIN::prepare(TABLE_LIST *tables_init, COND *conds_init, uint og_num,
  unit= unit_arg;
  if (prepare_stage2())
    goto err;
+  prepared= true;

  DBUG_RETURN(0); // All OK

@ -5185,7 +5187,8 @@ mysql_select(THD *thd, TABLE_LIST *tables, List<Item> &fields, COND *conds,
      }
      else
      {
-        if ((err= join->prepare(tables, conds, og_num, order, false, group,
+        if (!join->prepared &&
+            (err= join->prepare(tables, conds, og_num, order, false, group,
                                having, proc_param, select_lex, unit)))
 	{
 	  goto err;
@ -5211,7 +5214,8 @@ mysql_select(THD *thd, TABLE_LIST *tables, List<Item> &fields, COND *conds,
 	DBUG_RETURN(TRUE);
    THD_STAGE_INFO(thd, stage_init);
    thd->lex->used_tables=0;
-    if ((err= join->prepare(tables, conds, og_num, order, false, group, having,
+    if (!join->prepared &&
+        (err= join->prepare(tables, conds, og_num, order, false, group, having,
                            proc_param, select_lex, unit)))
    {
      goto err;
--- a/sql/sql_select.h
+++ b/sql/sql_select.h
@ -1596,6 +1596,8 @@ public:
  */
  bool impossible_where; 

+  bool prepared;
+
  /*
    All fields used in the query processing.

--- a/sql/sql_union.cc
+++ b/sql/sql_union.cc
@ -1759,24 +1759,6 @@ bool st_select_lex_unit::prepare(TABLE_LIST *derived_arg,
    goto err;

 cont:
-  pushdown_unit= find_unit_handler(thd, this);
-  if (pushdown_unit)
-  {
-    if (unlikely(pushdown_unit->prepare()))
-      goto err;
-    /*
-      Always use select_union_direct result for pushed down units, overwrite
-      the previous union_result unless select_union_direct is already used
-    */
-    if (!use_direct_union_result)
-    {
-      if (unlikely(set_direct_union_result(sel_result)))
-        goto err;
-      fake_select_lex= NULL;
-      instantiate_tmp_table= false;
-      use_direct_union_result= true;
-    }
-  }
  /*
    If the query is using select_union_direct, we have postponed
    preparation of the underlying select_result until column types
@ -1919,37 +1901,6 @@ cont:

      if (unlikely(saved_error))
        goto err;
-
-      if (fake_select_lex != NULL &&
-          (thd->stmt_arena->is_stmt_prepare() ||
-           (thd->lex->context_analysis_only & CONTEXT_ANALYSIS_ONLY_VIEW)))
-      {
-        /* Validate the global parameters of this union */
-
-	init_prepare_fake_select_lex(thd, TRUE);
-        /* Should be done only once (the only item_list per statement) */
-        DBUG_ASSERT(fake_select_lex->join == 0);
-	if (!(fake_select_lex->join= new JOIN(thd, item_list, thd->variables.option_bits,
-					      result)))
-	{
-	  fake_select_lex->table_list.empty();
-	  DBUG_RETURN(TRUE);
-	}
-
-        /*
-          Fake st_select_lex should have item list for correct ref_array
-          allocation.
-        */
-	fake_select_lex->item_list= item_list;
-
-	thd->lex->current_select= fake_select_lex;
-
-        /*
-          We need to add up n_sum_items in order to make the correct
-          allocation in setup_ref_array().
-        */
-        fake_select_lex->n_child_sum_items+= global_parameters()->n_sum_items;
-      }
    }
    else
    {
@ -1959,23 +1910,45 @@ cont:
      */
      table->reset_item_list(&item_list, hidden);
    }
-    if (fake_select_lex != NULL &&
-        (thd->stmt_arena->is_stmt_prepare() ||
-         (thd->lex->context_analysis_only & CONTEXT_ANALYSIS_ONLY_VIEW)))
+
+    if (fake_select_lex != NULL)
    {
-      if (!fake_select_lex->join &&
-          !(fake_select_lex->join=
-            new JOIN(thd, item_list, thd->variables.option_bits, result)))
+      init_prepare_fake_select_lex(thd, TRUE);
+
+      DBUG_ASSERT(fake_select_lex->join == 0);
+      if (!(fake_select_lex->join= new JOIN(thd, item_list, options, result)))
      {
-         fake_select_lex->table_list.empty();
-         DBUG_RETURN(TRUE);
+        fake_select_lex->table_list.empty();
+        DBUG_RETURN(TRUE);
      }
-      saved_error= fake_select_lex->join->
-        prepare(fake_select_lex->table_list.first, 0,
+
+      /*
+        Fake st_select_lex should have item list for correct ref_array
+        allocation.
+      */
+      fake_select_lex->item_list= item_list;
+
+      thd->lex->current_select= fake_select_lex;
+
+      /*
+        We need to add up n_sum_items in order to make the correct
+        allocation in setup_ref_array().
+      */
+      fake_select_lex->n_child_sum_items+= global_parameters()->n_sum_items;
+      fake_select_lex->join->no_const_tables= TRUE;
+      saved_error= fake_select_lex->join->prepare(
+          fake_select_lex->table_list.first, 0,
                global_parameters()->order_list.elements, // og_num
                global_parameters()->order_list.first,    // order
                false, NULL, NULL, NULL, fake_select_lex, this);
-      fake_select_lex->table_list.empty();
+    }
+
+    if (!thd->lex->is_view_context_analysis())
+      pushdown_unit= find_unit_handler(thd, this);
+    if (pushdown_unit)
+    {
+      if (prepare_pushdown(use_direct_union_result, sel_result))
+        goto err;
    }
  }

@ -1989,6 +1962,36 @@ err:
  DBUG_RETURN(TRUE);
 }

+/**
+  @brief
+    Prepare st_select_lex_unit for the pushdown handler processing
+  @details
+    Creates and initializes data structures required for processing of the
+    pushdown handler. Validates fake_select_lex then discards it and sets
+    direct union result which is necessary for pushed down statements
+  @return
+    false - success
+    true - failure
+*/
+bool st_select_lex_unit::prepare_pushdown(bool use_direct_union_result,
+                                          select_result *sel_result)
+{
+  if (unlikely(pushdown_unit->prepare()))
+    return true;
+
+  if(!use_direct_union_result)
+  {
+    /*
+      Always use select_union_direct result for pushed down units, overwrite
+      the previous union_result unless select_union_direct is already used
+    */
+    if (unlikely(set_direct_union_result(sel_result)))
+      return true;
+  }
+  return false;
+}
+
+
 bool st_select_lex_unit::set_direct_union_result(select_result *sel_result)
 {
  SELECT_LEX *last= first_select();
@ -2466,45 +2469,13 @@ bool st_select_lex_unit::exec_inner()
       saved_error= true;

      set_limit(global_parameters());
-      init_prepare_fake_select_lex(thd, first_execution);
      JOIN *join= fake_select_lex->join;
      saved_error= false;
-      if (!join)
+      if (!(thd->stmt_arena->is_stmt_prepare() ||
+           (thd->lex->context_analysis_only & CONTEXT_ANALYSIS_ONLY_VIEW)) &&
+          first_execution)
      {
-	/*
-	  allocate JOIN for fake select only once (prevent
-	  mysql_select automatic allocation)
-          TODO: The above is nonsense. mysql_select() will not allocate the
-          join if one already exists. There must be some other reason why we
-          don't let it allocate the join. Perhaps this is because we need
-          some special parameter values passed to join constructor?
-	*/
-	if (unlikely(!(fake_select_lex->join=
-                       new JOIN(thd, item_list, fake_select_lex->options,
-                                result))))
-	{
-	  fake_select_lex->table_list.empty();
-	  goto err;
-	}
-        fake_select_lex->join->no_const_tables= TRUE;
-
-        /*
-          Fake st_select_lex should have item list for correct ref_array
-          allocation.
-        */
-        fake_select_lex->item_list= item_list;
-
-        /*
-          We need to add up n_sum_items in order to make the correct
-          allocation in setup_ref_array().
-          Don't add more sum_items if we have already done JOIN::prepare
-          for this (with a different join object)
-        */
-        if (fake_select_lex->ref_pointer_array.is_null())
-          fake_select_lex->n_child_sum_items+= global_parameters()->n_sum_items;
-        
-        if (!was_executed)
-          save_union_explain_part2(thd->lex->explain);
+        save_union_explain_part2(thd->lex->explain);

        saved_error= mysql_select(thd, &result_table_list,
                                  item_list, NULL,
@ -2527,7 +2498,6 @@ bool st_select_lex_unit::exec_inner()
            subquery execution rather than EXPLAIN line production. In order 
            to reset them back, we re-do all of the actions (yes it is ugly):
          */ // psergey-todo: is the above really necessary anymore?? 
-	  join->init(thd, item_list, fake_select_lex->options, result);
          saved_error= mysql_select(thd, &result_table_list, item_list, NULL,
 				    global_parameters()->order_list.elements,
 				    global_parameters()->order_list.first,
@ -2557,7 +2527,6 @@ bool st_select_lex_unit::exec_inner()
    }
  }
  thd->lex->current_select= lex_select_save;
-err:
  thd->lex->set_limit_rows_examined();
  return saved_error;
 }
@ -2822,12 +2791,9 @@ bool st_select_lex_unit::change_result(select_result_interceptor *new_result,
      if (sl->join->change_result(new_result, old_result))
 	return true; /* purecov: inspected */
  }
-  /*
-    If there were a fake_select_lex->join, we would have to change the
-    result of that also, but change_result() is called before such an
-    object is created.
-  */
-  DBUG_ASSERT(fake_select_lex == NULL || fake_select_lex->join == NULL);
+
+  if (fake_select_lex && fake_select_lex->join)
+    fake_select_lex->join->change_result(new_result, old_result);
  return false;
 }