MDEV-25108: Running of the EXPLAIN EXTENDED statement produces extra warning in case it is executed in PS (prepared statement) modebb-10.2-MDEV-25108-1

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, 20 insertions, 0 deletions

diff --git a/mysql-test/t/ps.test b/mysql-test/t/ps.test
index a267c8b0e42..5b86f82a9cb 100644
--- a/mysql-test/t/ps.test
+++ b/mysql-test/t/ps.test
@@ -4927,5 +4927,25 @@ 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 #