MDEV-7828 Assertion `key_read == 0' failed in TABLE::enable_keyread with SELECT SQ and WHERE SQ

already fixed by a7ed4644a6.
just add a test case,

mysql-test/r/subselect.result

@@ -7138,3 +7138,11 @@ SELECT ( SELECT MAX(f1) FROM t2 ) FROM t1;
 ERROR 21000: Subquery returns more than 1 row
 drop view v1;
 drop table t1,t2;
+CREATE TABLE t1 (f1 INT, KEY(f1)) ENGINE=MyISAM;
+INSERT t1 VALUES (4),(8);
+CREATE TABLE t2 (f2 INT, KEY(f2)) ENGINE=MyISAM;
+INSERT t2 VALUES (6),(9);
+SELECT (SELECT MAX(sq.f2) FROM t1) FROM (SELECT * FROM t2) AS sq WHERE f2 = 2;
+(SELECT MAX(sq.f2) FROM t1)
+NULL
+drop table t1, t2;

mysql-test/r/subselect_no_mat.result

@@ -7135,6 +7135,14 @@ SELECT ( SELECT MAX(f1) FROM t2 ) FROM t1;
 ERROR 21000: Subquery returns more than 1 row
 drop view v1;
 drop table t1,t2;
+CREATE TABLE t1 (f1 INT, KEY(f1)) ENGINE=MyISAM;
+INSERT t1 VALUES (4),(8);
+CREATE TABLE t2 (f2 INT, KEY(f2)) ENGINE=MyISAM;
+INSERT t2 VALUES (6),(9);
+SELECT (SELECT MAX(sq.f2) FROM t1) FROM (SELECT * FROM t2) AS sq WHERE f2 = 2;
+(SELECT MAX(sq.f2) FROM t1)
+NULL
+drop table t1, t2;
 set optimizer_switch=default;
 select @@optimizer_switch like '%materialization=on%';
 @@optimizer_switch like '%materialization=on%'

mysql-test/r/subselect_no_opts.result

@@ -7133,4 +7133,12 @@ SELECT ( SELECT MAX(f1) FROM t2 ) FROM t1;
 ERROR 21000: Subquery returns more than 1 row
 drop view v1;
 drop table t1,t2;
+CREATE TABLE t1 (f1 INT, KEY(f1)) ENGINE=MyISAM;
+INSERT t1 VALUES (4),(8);
+CREATE TABLE t2 (f2 INT, KEY(f2)) ENGINE=MyISAM;
+INSERT t2 VALUES (6),(9);
+SELECT (SELECT MAX(sq.f2) FROM t1) FROM (SELECT * FROM t2) AS sq WHERE f2 = 2;
+(SELECT MAX(sq.f2) FROM t1)
+NULL
+drop table t1, t2;
 set @optimizer_switch_for_subselect_test=null;

mysql-test/r/subselect_no_scache.result

@@ -7144,6 +7144,14 @@ SELECT ( SELECT MAX(f1) FROM t2 ) FROM t1;
 ERROR 21000: Subquery returns more than 1 row
 drop view v1;
 drop table t1,t2;
+CREATE TABLE t1 (f1 INT, KEY(f1)) ENGINE=MyISAM;
+INSERT t1 VALUES (4),(8);
+CREATE TABLE t2 (f2 INT, KEY(f2)) ENGINE=MyISAM;
+INSERT t2 VALUES (6),(9);
+SELECT (SELECT MAX(sq.f2) FROM t1) FROM (SELECT * FROM t2) AS sq WHERE f2 = 2;
+(SELECT MAX(sq.f2) FROM t1)
+NULL
+drop table t1, t2;
 set optimizer_switch=default;
 select @@optimizer_switch like '%subquery_cache=on%';
 @@optimizer_switch like '%subquery_cache=on%'

mysql-test/r/subselect_no_semijoin.result

@@ -7133,5 +7133,13 @@ SELECT ( SELECT MAX(f1) FROM t2 ) FROM t1;
 ERROR 21000: Subquery returns more than 1 row
 drop view v1;
 drop table t1,t2;
+CREATE TABLE t1 (f1 INT, KEY(f1)) ENGINE=MyISAM;
+INSERT t1 VALUES (4),(8);
+CREATE TABLE t2 (f2 INT, KEY(f2)) ENGINE=MyISAM;
+INSERT t2 VALUES (6),(9);
+SELECT (SELECT MAX(sq.f2) FROM t1) FROM (SELECT * FROM t2) AS sq WHERE f2 = 2;
+(SELECT MAX(sq.f2) FROM t1)
+NULL
+drop table t1, t2;
 set @optimizer_switch_for_subselect_test=null;
 set @join_cache_level_for_subselect_test=NULL;

mysql-test/t/subselect.test

@@ -6023,3 +6023,13 @@ SELECT ( SELECT MAX(f1) FROM t2 ) FROM t1;
 
 drop view v1;
 drop table t1,t2;
+
+#
+# MDEV-7828 Assertion `key_read == 0' failed in TABLE::enable_keyread with SELECT SQ and WHERE SQ
+#
+CREATE TABLE t1 (f1 INT, KEY(f1)) ENGINE=MyISAM;
+INSERT t1 VALUES (4),(8);
+CREATE TABLE t2 (f2 INT, KEY(f2)) ENGINE=MyISAM;
+INSERT t2 VALUES (6),(9);
+SELECT (SELECT MAX(sq.f2) FROM t1) FROM (SELECT * FROM t2) AS sq WHERE f2 = 2;
+drop table t1, t2;