MDEV-21887: federatedx crashes on SELECT ... INTO query in select_handler code

Backport to 10.4:

- Don't try to push down SELECTs that have a side effect

- In case the storage engine did support pushdown of SELECT with an INTO
  clause, write the rows we've got from it into select->join->result,
  and not thd->protocol.  This way, SELECT ... INTO ... FROM
  smart_engine_table will put the result into where instructed, and
  NOT send it to the client.

2 files changed, 41 insertions, 2 deletions

diff --git a/mysql-test/suite/federated/federatedx_create_handlers.result b/mysql-test/suite/federated/federatedx_create_handlers.result
index 473972c2cd4..65a9d52803f 100644
--- a/mysql-test/suite/federated/federatedx_create_handlers.result
+++ b/mysql-test/suite/federated/federatedx_create_handlers.result
@@ -299,7 +299,27 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t3	ALL	NULL	NULL	NULL	NULL	7	
 1	PRIMARY	<derived2>	ref	key0	key0	18	federated.t3.name	2	
 2	PUSHED DERIVED	NULL	NULL	NULL	NULL	NULL	NULL	NULL	NULL
-DROP TABLE federated.t1, federated.t2, federated.t3;
+#
+# MDEV-21887: federatedx crashes on SELECT ... INTO query in select_handler code
+#
+CREATE TABLE federated.t4 (
+id int(20) NOT NULL,
+name varchar(16) NOT NULL default ''
+) engine=myisam;
+insert into federated.t4 select * from federated.t1;
+select * from federated.t4;
+id	name
+1	zzz
+3	xxx
+4	xxx
+5	yyy
+7	yyy
+select name into @var from federated.t1 where id=3 limit 1 ;
+select @var;
+@var
+xxx
+select name into outfile 'tmp.txt' from federated.t1;
+DROP TABLE federated.t1, federated.t2, federated.t3, federated.t4;
 connection slave;
 DROP TABLE federated.t1, federated.t2;
 connection default;
diff --git a/mysql-test/suite/federated/federatedx_create_handlers.test b/mysql-test/suite/federated/federatedx_create_handlers.test
index 373b2aaaa33..42a03e60d67 100644
--- a/mysql-test/suite/federated/federatedx_create_handlers.test
+++ b/mysql-test/suite/federated/federatedx_create_handlers.test
@@ -147,8 +147,27 @@ FROM federated.t3,
        SELECT * FROM federated.t1 WHERE id >= 5) t
 WHERE federated.t3.name=t.name;
 
+--echo #
+--echo # MDEV-21887: federatedx crashes on SELECT ... INTO query in select_handler code
+--echo #
 
-DROP TABLE federated.t1, federated.t2, federated.t3;
+CREATE TABLE federated.t4 (
+  id int(20) NOT NULL,
+  name varchar(16) NOT NULL default ''
+) engine=myisam;
+insert into federated.t4 select * from federated.t1;
+
+--sorted_result
+select * from federated.t4;
+
+select name into @var from federated.t1 where id=3 limit 1 ;
+select @var;
+select name into outfile 'tmp.txt' from federated.t1;
+
+let $path=`select concat(@@datadir, 'test/tmp.txt')`;
+remove_file $path;
+
+DROP TABLE federated.t1, federated.t2, federated.t3, federated.t4;
 
 connection slave;
 DROP TABLE federated.t1, federated.t2;