MDEV-25108: Running of the EXPLAIN EXTENDED statement produces extra warning in case it is executed in PS (prepared statement) mode

The EXPLAIN EXTENDED statement run as a prepared statement can produce extra
warning comparing with a case when EXPLAIN EXTENDED statement is run as
a regular statement. For example, the following test case
  CREATE TABLE t1 (c int);
  CREATE TABLE t2 (d int);
  EXPLAIN EXTENDED SELECT (SELECT 1 FROM t2 WHERE d = c) FROM t1;

produces the extra warning
  "Field or reference 'c' of SELECT #2 was resolved in SELECT #1"
in case the above mentioned "EXPLAIN EXTENDED" statement is executed
in PS mode, that is by submitting the following statements:
   PREPARE stmt FROM "EXPLAIN EXTENDED SELECT (SELECT 1 FROM t2 WHERE d = c) FROM t1";
   EXECUTE stmt;

The reason of the extra warning emittion is in a way items
are handled (being fixed) during execution of the JOIN::prepare() method.
The method Item_field::fix_fields() calls the find_field_in_tables()
function in case a field hasn't been associated yet with the item.
Implementation of the find_field_in_tables() function first checks whether
a table containing the required field was already opened and cached.
It is done by checking the data member item->cached_table. This data member
is set on handling the PRERARE FROM statement and checked on executing
the EXECUTE statement. If the data member item->cached_table is set
the find_field_in_tables() function invoked and the
mark_select_range_as_dependent() function called if the field
is an outer referencee. The mark_select_range_as_dependent() function
calls the mark_as_dependent() function that finally invokes
the push_warning_printf() function that produces extra warning.

To fix the issue, calling of push_warning_printf() is elimited in case
it was run indirectly in result of hanlding already opened table from
the Item_field::fix_fields() method.

Author: dmitryshulga

mysql-test/r/ps.result

@@ -5419,5 +5419,42 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 DEALLOCATE PREPARE stmt;
 DROP TABLE t1;
 #
+# MDEV-25108: Running of the EXPLAIN EXTENDED statement produces extra warning
+#             in case it is executed in PS (prepared statement) mode
+#
+CREATE TABLE t1 (c int);
+CREATE TABLE t2 (d int);
+# EXPLAIN EXTENDED in regular way (not PS mode)
+EXPLAIN EXTENDED SELECT (SELECT 1 FROM t2 WHERE d = c) FROM t1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	PRIMARY	t1	system	NULL	NULL	NULL	NULL	0	0.00	const row not found
+2	SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE noticed after reading const tables
+Warnings:
+Note	1276	Field or reference 'test.t1.c' of SELECT #2 was resolved in SELECT #1
+Note	1003	select (select 1 from `test`.`t2` where 0) AS `(SELECT 1 FROM t2 WHERE d = c)` from `test`.`t1`
+SHOW WARNINGS;
+Level	Code	Message
+Note	1276	Field or reference 'test.t1.c' of SELECT #2 was resolved in SELECT #1
+Note	1003	select (select 1 from `test`.`t2` where 0) AS `(SELECT 1 FROM t2 WHERE d = c)` from `test`.`t1`
+# Now run the same EXPLAIN EXTENDED in PS mode. Number of warnings
+# and their content must be the same as in case running the statement
+# in regular way
+PREPARE stmt FROM "EXPLAIN EXTENDED SELECT (SELECT 1 FROM t2 WHERE d = c) FROM t1";
+Warnings:
+Note	1276	Field or reference 'test.t1.c' of SELECT #2 was resolved in SELECT #1
+EXECUTE stmt;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	PRIMARY	t1	system	NULL	NULL	NULL	NULL	0	0.00	const row not found
+2	SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE noticed after reading const tables
+Warnings:
+Note	1276	Field or reference 'test.t1.c' of SELECT #2 was resolved in SELECT #1
+Note	1003	select (select 1 from `test`.`t2` where 0) AS `(SELECT 1 FROM t2 WHERE d = c)` from `test`.`t1`
+SHOW WARNINGS;
+Level	Code	Message
+Note	1276	Field or reference 'test.t1.c' of SELECT #2 was resolved in SELECT #1
+Note	1003	select (select 1 from `test`.`t2` where 0) AS `(SELECT 1 FROM t2 WHERE d = c)` from `test`.`t1`
+DEALLOCATE PREPARE stmt;
+DROP TABLE t1, t2;
+#
 # End of 10.2 tests
 #

mysql-test/t/ps.test

@@ -4926,6 +4926,26 @@ EXECUTE stmt;
 DEALLOCATE PREPARE stmt;
 DROP TABLE t1;
 
+--echo #
+--echo # MDEV-25108: Running of the EXPLAIN EXTENDED statement produces extra warning
+--echo #             in case it is executed in PS (prepared statement) mode
+--echo #
+CREATE TABLE t1 (c int);
+CREATE TABLE t2 (d int);
+
+--echo # EXPLAIN EXTENDED in regular way (not PS mode)
+EXPLAIN EXTENDED SELECT (SELECT 1 FROM t2 WHERE d = c) FROM t1;
+SHOW WARNINGS;
+
+--echo # Now run the same EXPLAIN EXTENDED in PS mode. Number of warnings
+--echo # and their content must be the same as in case running the statement
+--echo # in regular way
+PREPARE stmt FROM "EXPLAIN EXTENDED SELECT (SELECT 1 FROM t2 WHERE d = c) FROM t1";
+EXECUTE stmt;
+SHOW WARNINGS;
+
+DEALLOCATE PREPARE stmt;
+DROP TABLE t1, t2;
 --echo #
 --echo # End of 10.2 tests
 --echo #

sql/item.cc

@@ -4668,11 +4668,14 @@ bool Item_ref_null_helper::get_date(MYSQL_TIME *ltime, ulonglong fuzzydate)
   @param resolved_item   item which was resolved in outer SELECT(for warning)
   @param mark_item       item which should be marked (can be differ in case of
                          substitution)
+  @param suppress_warning_output  flag specifying whether to suppress output of
+                                  a warning message
 */
 
 static bool mark_as_dependent(THD *thd, SELECT_LEX *last, SELECT_LEX *current,
                               Item_ident *resolved_item,
-                              Item_ident *mark_item)
+                              Item_ident *mark_item,
+                              bool suppress_warning_output)
 {
   DBUG_ENTER("mark_as_dependent");
 
@@ -4685,7 +4688,7 @@ static bool mark_as_dependent(THD *thd, SELECT_LEX *last, SELECT_LEX *current,
   if (current->mark_as_dependent(thd, last,
                                  /** resolved_item psergey-thu **/ mark_item))
     DBUG_RETURN(TRUE);
-  if (thd->lex->describe & DESCRIBE_EXTENDED)
+  if ((thd->lex->describe & DESCRIBE_EXTENDED) && !suppress_warning_output)
   {
     const char *db_name= (resolved_item->db_name ?
                           resolved_item->db_name : "");
@@ -4714,6 +4717,8 @@ static bool mark_as_dependent(THD *thd, SELECT_LEX *last, SELECT_LEX *current,
   @param found_item      Item which was found during resolving (if resolved
                          identifier belongs to VIEW)
   @param resolved_item   Identifier which was resolved
+  @param suppress_warning_output  flag specifying whether to suppress output of
+                                  a warning message
 
   @note
     We have to mark all items between current_sel (including) and
@@ -4727,7 +4732,8 @@ void mark_select_range_as_dependent(THD *thd,
                                     SELECT_LEX *last_select,
                                     SELECT_LEX *current_sel,
                                     Field *found_field, Item *found_item,
-                                    Item_ident *resolved_item)
+                                    Item_ident *resolved_item,
+                                    bool suppress_warning_output)
 {
   /*
     Go from current SELECT to SELECT where field was resolved (it
@@ -4762,7 +4768,7 @@ void mark_select_range_as_dependent(THD *thd,
         found_field->table->map;
     prev_subselect_item->const_item_cache= 0;
     mark_as_dependent(thd, last_select, current_sel, resolved_item,
-                      dependent);
+                      dependent, suppress_warning_output);
   }
 }
 
@@ -5228,7 +5234,7 @@ Item_field::fix_outer_field(THD *thd, Field **from_field, Item **reference)
                               context->select_lex, this,
                               ((ref_type == REF_ITEM ||
                                 ref_type == FIELD_ITEM) ?
-                               (Item_ident*) (*reference) : 0));
+                               (Item_ident*) (*reference) : 0), false);
             return 0;
           }
         }
@@ -5240,7 +5246,7 @@ Item_field::fix_outer_field(THD *thd, Field **from_field, Item **reference)
                             context->select_lex, this,
                             ((ref_type == REF_ITEM || ref_type == FIELD_ITEM) ?
                              (Item_ident*) (*reference) :
-                             0));
+                             0), false);
           if (thd->lex->in_sum_func &&
               thd->lex->in_sum_func->nest_level >= select->nest_level)
           {
@@ -5354,7 +5360,7 @@ Item_field::fix_outer_field(THD *thd, Field **from_field, Item **reference)
     set_max_sum_func_level(thd, select);
     mark_as_dependent(thd, last_checked_context->select_lex,
                       context->select_lex, rf,
-                      rf);
+                      rf, false);
 
     return 0;
   }
@@ -5367,7 +5373,7 @@ Item_field::fix_outer_field(THD *thd, Field **from_field, Item **reference)
     set_max_sum_func_level(thd, select);
     mark_as_dependent(thd, last_checked_context->select_lex,
                       context->select_lex,
-                      this, (Item_ident*)*reference);
+                      this, (Item_ident*)*reference, false);
     if (last_checked_context->select_lex->having_fix_field)
     {
       Item_ref *rf;
@@ -7401,7 +7407,7 @@ class Dependency_marker: public Field_enumerator
         if (tbl->table == item->field->table)
         {
           if (sel != current_select)
-            mark_as_dependent(thd, sel, current_select, item, item);
+            mark_as_dependent(thd, sel, current_select, item, item, false);
           return;
         }
       }
@@ -7596,7 +7602,7 @@ bool Item_ref::fix_fields(THD *thd, Item **reference)
                               ((refer_type == REF_ITEM ||
                                 refer_type == FIELD_ITEM) ?
                                (Item_ident*) (*reference) :
-                               0));
+                               0), false);
             /*
               view reference found, we substituted it instead of this
               Item, so can quit
@@ -7646,7 +7652,7 @@ bool Item_ref::fix_fields(THD *thd, Item **reference)
           goto error;
         thd->change_item_tree(reference, fld);
         mark_as_dependent(thd, last_checked_context->select_lex,
-                          current_sel, fld, fld);
+                          current_sel, fld, fld, false);
         /*
           A reference is resolved to a nest level that's outer or the same as
           the nest level of the enclosing set function : adjust the value of
@@ -7669,7 +7675,7 @@ bool Item_ref::fix_fields(THD *thd, Item **reference)
       /* Should be checked in resolve_ref_in_select_and_group(). */
       DBUG_ASSERT(*ref && (*ref)->fixed);
       mark_as_dependent(thd, last_checked_context->select_lex,
-                        context->select_lex, this, this);
+                        context->select_lex, this, this, false);
       /*
         A reference is resolved to a nest level that's outer or the same as
         the nest level of the enclosing set function : adjust the value of

sql/item.h

@@ -6088,7 +6088,8 @@ void mark_select_range_as_dependent(THD *thd,
                                     st_select_lex *last_select,
                                     st_select_lex *current_sel,
                                     Field *found_field, Item *found_item,
-                                    Item_ident *resolved_item);
+                                    Item_ident *resolved_item,
+                                    bool suppress_warning_output);
 
 extern Cached_item *new_Cached_item(THD *thd, Item *item,
                                     bool pass_through_ref);

sql/item_subselect.h

@@ -283,7 +283,8 @@ class Item_subselect :public Item_result_field,
   friend bool Item_ref::fix_fields(THD *, Item **);
   friend void mark_select_range_as_dependent(THD*,
                                              st_select_lex*, st_select_lex*,
-                                             Field*, Item*, Item_ident*);
+                                             Field*, Item*, Item_ident*,
+                                             bool);
   friend bool convert_join_subqueries_to_semijoins(JOIN *join);
 };
 

sql/sql_base.cc

@@ -6046,7 +6046,7 @@ find_field_in_tables(THD *thd, Item_ident *item,
         if (!all_merged && current_sel != last_select)
         {
           mark_select_range_as_dependent(thd, last_select, current_sel,
-                                         found, *ref, item);
+                                         found, *ref, item, true);
         }
       }
       return found;