MDEV-25108: Running of the EXPLAIN EXTENDED statement produces extra warning in case it is executed in PS (prepared statement) modebb-10.2-MDEV-25108

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.

1 files changed, 2 insertions, 1 deletions

diff --git a/sql/item_subselect.h b/sql/item_subselect.h
index 9116238c640..de21f00143f 100644
--- a/sql/item_subselect.h
+++ b/sql/item_subselect.h
@@ -279,7 +279,8 @@ public:
   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);
 };