MDEV-32382 FederatedX error on pushdown of statements having CTE

Pushing down statements to FederatedX engine is implemented by
printing either SELECT_LEX or SELECT_LEX_UNIT into a string and
sending that string to the engine. In the case of pushing down a
single SELECT having a CTE (WITH clause) there was a problem, because
normally single SELECTs were printed using SELECT_LEX::print().
But CTEs are stored in the upper unit of the SELECT_LEX -
SELECT_LEX_UNIT, so they were not unfolded in the string produced.

The solution is to invoke SELECT_LEX_UNIT::print() when pushing down
single SELECT statements (but not those which are parts of units),
so the possible CTEs are unfolded and printed.

Reviewed by Sergei Petrunia (sergey@mariadb.com)

mysql-test/suite/federated/federatedx_create_handlers.result

@@ -1140,6 +1140,111 @@ t3_myisam2
 t3_myisam3
 SELECT * FROM federated.t1 UNION SELECT * FROM t3 ORDER BY 2;
 ERROR 42S22: Unknown column '2' in 'order clause'
+#
+# MDEV-32382 FederatedX error on pushdown of statement having CTE
+#
+# Single SELECT with CTE
+WITH cte AS (SELECT * FROM federated.t1)
+SELECT * FROM cte;
+a
+bcd
+abc
+cde
+explain extended WITH cte AS (SELECT * FROM federated.t1)
+SELECT * FROM cte;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	PUSHED SELECT	NULL	NULL	NULL	NULL	NULL	NULL	NULL	NULL	NULL
+Warnings:
+Note	1003	with cte as (/* select#2 */ select `federated`.`t1`.`a` AS `a` from `federated`.`t1`)/* select#1 */ select `cte`.`a` AS `a` from `cte`
+# Pushdown of a UNION having CTE's
+WITH cte AS (SELECT * FROM federated.t1),
+cte2 AS (SELECT * FROM federated.t2)
+SELECT * FROM cte
+UNION
+SELECT * FROM cte2;
+a
+abc
+bcd
+cde
+def
+efg
+explain extended WITH cte AS (SELECT * FROM federated.t1),
+cte2 AS (SELECT * FROM federated.t2)
+SELECT * FROM cte
+UNION
+SELECT * FROM cte2;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+NULL	PUSHED UNION	NULL	NULL	NULL	NULL	NULL	NULL	NULL	NULL	NULL
+Warnings:
+Note	1003	with cte as (/* select#2 */ select `federated`.`t1`.`a` AS `a` from `federated`.`t1`), cte2 as (/* select#3 */ select `federated`.`t2`.`a` AS `a` from `federated`.`t2`)/* select#1 */ select `cte`.`a` AS `a` from `cte` union /* select#4 */ select `cte2`.`a` AS `a` from `cte2`
+# Partial pushdown is not allowed for unions with CTE's, however a CTE
+# may be pushed down a derived table
+WITH cte AS (SELECT * FROM federated.t1)
+SELECT * FROM cte
+UNION ALL
+SELECT * FROM t3;
+a
+abc
+bcd
+cde
+t3_myisam1
+t3_myisam2
+t3_myisam3
+explain extended WITH cte AS (SELECT * FROM federated.t1)
+SELECT * FROM cte
+UNION ALL
+SELECT * FROM t3;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	PRIMARY	<derived2>	ALL	NULL	NULL	NULL	NULL	3	100.00	
+2	PUSHED DERIVED	NULL	NULL	NULL	NULL	NULL	NULL	NULL	NULL	NULL
+3	UNION	t3	ALL	NULL	NULL	NULL	NULL	3	100.00	
+Warnings:
+Note	1003	with cte as (/* select#2 */ select `federated`.`t1`.`a` AS `a` from `federated`.`t1`)/* select#1 */ select `cte`.`a` AS `a` from `cte` union all /* select#3 */ select `federated`.`t3`.`a` AS `a` from `federated`.`t3`
+WITH cte AS (SELECT * FROM federated.t1 UNION SELECT * FROM t3)
+SELECT * FROM cte;
+a
+abc
+bcd
+cde
+t3_myisam1
+t3_myisam2
+t3_myisam3
+explain extended WITH cte AS (SELECT * FROM federated.t1 UNION SELECT * FROM t3)
+SELECT * FROM cte;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	PRIMARY	<derived2>	ALL	NULL	NULL	NULL	NULL	6	100.00	
+2	DERIVED	t1	ALL	NULL	NULL	NULL	NULL	3	100.00	
+3	UNION	t3	ALL	NULL	NULL	NULL	NULL	3	100.00	
+NULL	UNION RESULT	<union2,3>	ALL	NULL	NULL	NULL	NULL	NULL	NULL	
+Warnings:
+Note	1003	with cte as (/* select#2 */ select `federated`.`t1`.`a` AS `a` from `federated`.`t1` union /* select#3 */ select `federated`.`t3`.`a` AS `a` from `federated`.`t3`)/* select#1 */ select `cte`.`a` AS `a` from `cte`
+# Two CTE's where one CTE refers to another
+WITH cte AS (SELECT * FROM federated.t1),
+cte2 AS (SELECT * FROM t3
+WHERE t3.a NOT IN (SELECT * FROM cte))
+SELECT * FROM cte JOIN cte2;
+a	a
+abc	t3_myisam1
+abc	t3_myisam2
+abc	t3_myisam3
+bcd	t3_myisam1
+bcd	t3_myisam2
+bcd	t3_myisam3
+cde	t3_myisam1
+cde	t3_myisam2
+cde	t3_myisam3
+explain extended WITH cte AS (SELECT * FROM federated.t1),
+cte2 AS (SELECT * FROM t3
+WHERE t3.a NOT IN (SELECT * FROM cte))
+SELECT * FROM cte JOIN cte2;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	PRIMARY	<derived5>	ALL	NULL	NULL	NULL	NULL	3	100.00	
+1	PRIMARY	t3	ALL	NULL	NULL	NULL	NULL	3	100.00	Using where; Using join buffer (flat, BNL join)
+5	PUSHED DERIVED	NULL	NULL	NULL	NULL	NULL	NULL	NULL	NULL	NULL
+4	MATERIALIZED	<derived2>	ALL	NULL	NULL	NULL	NULL	3	100.00	
+2	PUSHED DERIVED	NULL	NULL	NULL	NULL	NULL	NULL	NULL	NULL	NULL
+Warnings:
+Note	1003	with cte as (/* select#2 */ select `federated`.`t1`.`a` AS `a` from `federated`.`t1`), cte2 as (/* select#3 */ select `federated`.`t3`.`a` AS `a` from `federated`.`t3` where !<expr_cache><`federated`.`t3`.`a`>(<in_optimizer>(`federated`.`t3`.`a`,`federated`.`t3`.`a` in ( <materialize> (/* select#4 */ select `cte`.`a` from `cte` ), <primary_index_lookup>(`federated`.`t3`.`a` in <temporary table> on distinct_key where `federated`.`t3`.`a` = `<subquery4>`.`a`)))))/* select#1 */ select `cte`.`a` AS `a`,`federated`.`t3`.`a` AS `a` from `cte` join `federated`.`t3` where !<expr_cache><`federated`.`t3`.`a`>(<in_optimizer>(`federated`.`t3`.`a`,`federated`.`t3`.`a` in ( <materialize> (/* select#4 */ select `cte`.`a` from `cte` ), <primary_index_lookup>(`federated`.`t3`.`a` in <temporary table> on distinct_key where `federated`.`t3`.`a` = `<subquery4>`.`a`))))
 connection master;
 DROP TABLES federated.t1, federated.t2, t3, t4, t5, t6, federated.t11,
 federated.t12, federated.t13, federated.t14;

mysql-test/suite/federated/federatedx_create_handlers.test

@@ -740,6 +740,55 @@ SELECT * FROM federated.t1 UNION SELECT * FROM t3 ORDER BY a;
 SELECT * FROM federated.t1 UNION SELECT * FROM t3 ORDER BY 2;
 
 
+--echo #
+--echo # MDEV-32382 FederatedX error on pushdown of statement having CTE
+--echo #
+
+--echo # Single SELECT with CTE
+let $query= WITH cte AS (SELECT * FROM federated.t1)
+            SELECT * FROM cte;
+eval $query;
+eval explain extended $query;
+
+--echo # Pushdown of a UNION having CTE's
+let $query= WITH cte AS (SELECT * FROM federated.t1),
+  cte2 AS (SELECT * FROM federated.t2)
+  SELECT * FROM cte
+  UNION
+  SELECT * FROM cte2;
+--sorted_result
+eval $query;
+eval explain extended $query;
+
+# CREATE TABLE t3 (a int);
+# INSERT INTO t3 VALUES (101),(102),(103);
+
+--echo # Partial pushdown is not allowed for unions with CTE's, however a CTE
+--echo # may be pushed down a derived table
+let $query= WITH cte AS (SELECT * FROM federated.t1)
+  SELECT * FROM cte
+  UNION ALL
+  SELECT * FROM t3;
+--sorted_result
+eval $query;
+eval explain extended $query;
+
+let $query= WITH cte AS (SELECT * FROM federated.t1 UNION SELECT * FROM t3)
+  SELECT * FROM cte;
+--sorted_result
+eval $query;
+eval explain extended $query;
+
+--echo # Two CTE's where one CTE refers to another
+let $query= WITH cte AS (SELECT * FROM federated.t1),
+                 cte2 AS (SELECT * FROM t3
+                          WHERE t3.a NOT IN (SELECT * FROM cte))
+            SELECT * FROM cte JOIN cte2;
+--sorted_result
+eval $query;
+eval explain extended $query;
+
+
 # Cleanup
 connection master;
 DROP TABLES federated.t1, federated.t2, t3, t4, t5, t6, federated.t11,

sql/select_handler.cc

@@ -200,3 +200,18 @@ void select_handler::print_error(int error, myf errflag)
 {
   my_error(ER_GET_ERRNO, MYF(0), error, hton_name(ht)->str);
 }
+
+select_pushdown_type select_handler::get_pushdown_type()
+{
+  /*
+    In the case of single SELECT select_lex is initialized and lex_unit==NULL,
+    in the case of whole UNIT select_lex == NULL and lex_unit is initialized,
+    in the case of partial pushdown both select_lex and lex_unit
+      are initialized
+  */
+  if(!lex_unit)
+    return select_pushdown_type::SINGLE_SELECT;
+
+  return select_lex ? select_pushdown_type::PART_OF_UNIT :
+                      select_pushdown_type::WHOLE_UNIT;
+}

sql/select_handler.h

@@ -20,6 +20,12 @@
 #include "mariadb.h"
 #include "sql_priv.h"
 
+enum class select_pushdown_type {
+  SINGLE_SELECT,
+  PART_OF_UNIT,
+  WHOLE_UNIT
+};
+
 /**
   @class select_handler
 
@@ -50,7 +56,7 @@ class select_handler
   virtual bool prepare();
 
   /*
-    Select_handler processes one of
+    Select_handler processes these cases:
     - single SELECT
     - whole unit (multiple SELECTs combined with UNION/EXCEPT/INTERSECT)
     - single SELECT that is part of a unit (partial pushdown)
@@ -60,7 +66,7 @@ class select_handler
     in the case of partial pushdown both select_lex and lex_unit
       are initialized
   */
-  SELECT_LEX *select_lex;      // Single select to be executed
+  SELECT_LEX *select_lex;      // Single select/part of a unit to be executed
   SELECT_LEX_UNIT *lex_unit;   // Unit to be executed
 
   /*
@@ -99,6 +105,8 @@ class select_handler
 
   TABLE *create_tmp_table(THD *thd);
 
+  select_pushdown_type get_pushdown_type();
+
   THD *thd;
   handlerton *ht;
 

sql/sql_select.cc

@@ -5054,8 +5054,15 @@ select_handler *find_select_handler_inner(THD *thd,
                                     SELECT_LEX *select_lex,
                                     SELECT_LEX_UNIT *select_lex_unit)
 {
-  if (select_lex->master_unit()->outer_select())
+  if (select_lex->master_unit()->outer_select() ||
+      (select_lex_unit && select_lex->master_unit()->with_clause))
+  {
+    /*
+      Pushdown is not supported neither for non-top-level SELECTs nor for parts
+      of SELECT_LEX_UNITs that have CTEs (SELECT_LEX_UNIT::with_clause)
+    */
     return 0;
+  }
 
   TABLE_LIST *tbl= nullptr;
   // For SQLCOM_INSERT_SELECT the server takes TABLE_LIST

storage/federatedx/federatedx_pushdown.cc

@@ -276,18 +276,6 @@ federatedx_handler_base::federatedx_handler_base(THD *thd_arg, TABLE *tbl_arg)
    query_table(tbl_arg)
 {}
 
-ha_federatedx_select_handler::ha_federatedx_select_handler(
-    THD *thd, SELECT_LEX *select_lex, TABLE *tbl)
-  : select_handler(thd, federatedx_hton, select_lex),
-    federatedx_handler_base(thd, tbl)
-{
-  query.length(0);
-  select_lex->print(thd, &query,
-                    enum_query_type(QT_VIEW_INTERNAL |
-                                    QT_ITEM_ORIGINAL_FUNC_NULLIF |
-                                    QT_PARSABLE));
-}
-
 ha_federatedx_select_handler::~ha_federatedx_select_handler() = default;
 
 ha_federatedx_select_handler::ha_federatedx_select_handler(
@@ -296,10 +284,7 @@ ha_federatedx_select_handler::ha_federatedx_select_handler(
     federatedx_handler_base(thd, tbl)
 {
   query.length(0);
-  lex_unit->print(&query,
-                  enum_query_type(QT_VIEW_INTERNAL | QT_SELECT_ONLY |
-                                  QT_ITEM_ORIGINAL_FUNC_NULLIF |
-                                  QT_PARSABLE));
+  lex_unit->print(&query, PRINT_QUERY_TYPE);
 }
 
 ha_federatedx_select_handler::ha_federatedx_select_handler(
@@ -308,10 +293,31 @@ ha_federatedx_select_handler::ha_federatedx_select_handler(
       federatedx_handler_base(thd, tbl)
 {
   query.length(0);
-  select_lex->print(thd, &query,
-                    enum_query_type(QT_VIEW_INTERNAL | QT_SELECT_ONLY |
-                                    QT_ITEM_ORIGINAL_FUNC_NULLIF |
-                                    QT_PARSABLE));
+  if (get_pushdown_type() == select_pushdown_type::SINGLE_SELECT)
+  {
+    /*
+      Must use SELECT_LEX_UNIT::print() instead of SELECT_LEX::print() here
+      to print possible CTEs which are stored at SELECT_LEX_UNIT::with_clause
+    */
+    select_lex->master_unit()->print(&query, PRINT_QUERY_TYPE);
+  }
+  else if (get_pushdown_type() == select_pushdown_type::PART_OF_UNIT)
+  {
+    /*
+      CTEs are not supported for partial select pushdown so use
+      SELECT_LEX::print() here
+    */
+    select_lex->print(thd, &query, PRINT_QUERY_TYPE);
+  }
+  else
+  {
+    /*
+      Other select_pushdown_types are not allowed in this constructor.
+      The case of select_pushdown_type::WHOLE_UNIT is handled at another
+      overload of the constuctor
+    */
+    DBUG_ASSERT(0);
+  }
 }
 
 int federatedx_handler_base::init_scan_()

storage/federatedx/federatedx_pushdown.h

@@ -62,8 +62,6 @@ class ha_federatedx_derived_handler: public derived_handler, public federatedx_h
 class ha_federatedx_select_handler: public select_handler, public federatedx_handler_base
 {
 public:
-  ha_federatedx_select_handler(THD *thd_arg, SELECT_LEX *sel_lex,
-                               TABLE *tbl);
   ha_federatedx_select_handler(THD *thd_arg, SELECT_LEX_UNIT *sel_unit,
                                TABLE *tbl);
   ha_federatedx_select_handler(THD *thd_arg, SELECT_LEX *sel_lex,
@@ -72,4 +70,9 @@ class ha_federatedx_select_handler: public select_handler, public federatedx_han
   int init_scan() { return federatedx_handler_base::init_scan_(); }
   int next_row() { return federatedx_handler_base::next_row_(table); }
   int end_scan();
+
+private:
+  static constexpr auto PRINT_QUERY_TYPE=
+      enum_query_type(QT_VIEW_INTERNAL | QT_SELECT_ONLY |
+                      QT_ITEM_ORIGINAL_FUNC_NULLIF | QT_PARSABLE);
 };