1 files changed, 213 insertions, 0 deletions
diff --git a/mysql-test/main/derived_split_innodb.test b/mysql-test/main/derived_split_innodb.test
index 2f74f5fe747..a26c9af4e64 100644
--- a/mysql-test/main/derived_split_innodb.test
+++ b/mysql-test/main/derived_split_innodb.test
@@ -227,3 +227,216 @@ where t3.b > 15;
 drop table t3, t4;
 
 --echo # End of 10.3 tests
+
+--source include/have_sequence.inc
+
+--echo #
+--echo # MDEV-26301: Split optimization refills temporary table too many times
+--echo #
+
+# 5 values
+create table t1(a int, b int);
+insert into t1 select seq,seq from seq_1_to_5;
+
+# 5 value groups of size 2 each
+create table t2(a int, b int, key(a));
+insert into t2
+select A.seq,B.seq from seq_1_to_25 A, seq_1_to_2 B;
+
+# 5 value groups of size 3 each
+create table t3(a int, b int, key(a));
+insert into t3
+select A.seq,B.seq from seq_1_to_5 A, seq_1_to_3 B;
+
+analyze table t1,t2,t3 persistent for all;
+
+explain
+select * from
+  (t1 left join t2 on t2.a=t1.b) left join t3 on t3.a=t1.b;
+
+# Now, create tables for Groups.
+
+create table t10 (
+  grp_id int,
+  col1 int,
+  key(grp_id)
+);
+
+# 100 groups of 100 values each
+insert into t10
+select
+  A.seq,
+  B.seq
+from
+  seq_1_to_100 A,
+  seq_1_to_100 B;
+
+# and X10 multiplier
+
+create table t11 (
+  col1 int,
+  col2 int
+);
+insert into t11
+select A.seq, A.seq from seq_1_to_10 A;
+
+analyze table t10,t11 persistent for all;
+
+let $q1=
+select * from
+  (
+    (t1 left join t2 on t2.a=t1.b)
+    left join t3 on t3.a=t1.b
+  ) left join (select grp_id, count(*)
+               from t10 left join t11 on t11.col1=t10.col1
+               group by grp_id) T on T.grp_id=t1.b;
+
+eval
+explain $q1;
+
+--echo # The important part in the below output is:
+--echo #        "lateral": 1,
+--echo #        "query_block": {
+--echo #          "select_id": 2,
+--echo #          "r_loops": 5,  <-- must be 5, not 30.
+--source include/analyze-format.inc
+
+eval
+analyze format=json $q1;
+
+create table t21 (pk int primary key);
+insert into t21 values (1),(2),(3);
+
+create table t22 (pk int primary key);
+insert into t22 values (1),(2),(3);
+
+# Same as above but throw in a couple of const tables.
+explain
+select * from
+  t21, t22,
+  (
+    (t1 left join t2 on t2.a=t1.b)
+    left join t3 on t3.a=t1.b
+  ) left join (select grp_id, count(*)
+               from t10 left join t11 on t11.col1=t10.col1
+               group by grp_id) T on T.grp_id=t1.b
+where
+  t21.pk=1 and t22.pk=2;
+
+explain
+select * from
+  t21,
+  (
+    (t1 left join t2 on t2.a=t1.b)
+    left join t3 on t3.a=t1.b
+  ) left join (select grp_id, count(*)
+               from
+                 t22 join t10 left join t11 on t11.col1=t10.col1
+               where
+                 t22.pk=1
+               group by grp_id) T on T.grp_id=t1.b
+where
+  t21.pk=1;
+
+# And also add a non-const table
+
+create table t5 (
+  pk int primary key
+  );
+insert into t5 select seq from seq_1_to_1000;
+
+explain
+select * from
+  t21,
+  (
+    (((t1 join t5 on t5.pk=t1.b)) left join t2 on t2.a=t1.b)
+    left join t3 on t3.a=t1.b
+  ) left join (select grp_id, count(*)
+               from
+                 t22 join t10 left join t11 on t11.col1=t10.col1
+               where
+                 t22.pk=1
+               group by grp_id) T on T.grp_id=t1.b
+where
+  t21.pk=1;
+
+drop table t1,t2,t3,t5, t10, t11, t21, t22;
+
+# 5 values
+create table t1(a int, b int);
+insert into t1 select seq,seq from seq_1_to_5;
+
+# 5 value groups of size 2 each
+create table t2(a int, b int, key(a));
+insert into t2
+select A.seq,B.seq from seq_1_to_25 A, seq_1_to_2 B;
+
+# 5 value groups of size 3 each
+create table t3(a int, b int, key(a));
+insert into t3
+select A.seq,B.seq from seq_1_to_5 A, seq_1_to_3 B;
+
+analyze table t1,t2,t3 persistent for all;
+
+create table t10 (
+  grp_id int,
+  col1 int,
+  key(grp_id)
+);
+
+# 100 groups of 100 values each
+insert into t10
+select
+  A.seq,
+  B.seq
+from
+  seq_1_to_100 A,
+  seq_1_to_100 B;
+
+# and X10 multiplier
+
+create table t11 (
+  col1 int,
+  col2 int
+);
+insert into t11
+select A.seq, A.seq from seq_1_to_10 A;
+
+analyze table t10,t11 persistent for all;
+
+let $q=  
+select *
+from
+  (
+    (t1 left join t2 on t2.a=t1.b)
+     left join
+    t3
+    on t3.a=t1.b
+  ) 
+  left join
+  ( 
+    select grp_id, count(*)
+    from t10 left join t11 on t11.col1=t10.col1
+    group by grp_id
+  )dt
+  on dt.grp_id=t1.b;
+
+eval explain $q;
+eval $q;
+
+set join_cache_level=4;
+eval explain $q;
+eval $q;
+
+set join_cache_level=default;
+
+drop index a on t2;
+drop index a on t3;
+
+eval explain $q;
+eval $q;
+
+drop table t1,t2,t3;
+drop table t10, t11;
+
+--echo # End of 10.4 tests