Fixed mdev-14880: Assertion `inj_cond_list.elements' failed

in JOIN::inject_best_splitting_cond

The value of SplM_opt_info::last_plan should be set to NULL
before any search for a splitting plan for a splittable
materialized table.

mysql-test/r/derived_cond_pushdown.result

@@ -14788,3 +14788,68 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
 Warnings:
 Note	1003	with cte as (/* select#2 */ select `test`.`t1`.`pk` AS `pk` from `test`.`t1` where 0 group by `test`.`t1`.`pk`)/* select#1 */ select NULL AS `pk` from `cte`
 DROP TABLE t1;
+#
+# MDEV-14880: assertion failure in optimizer when splitting is applied
+#
+CREATE TABLE t1 (pk1 INT PRIMARY KEY, f INT) ENGINE=Aria;
+INSERT INTO t1 VALUES (1,0),(2,0);
+CREATE TABLE t2 (pk2 INT PRIMARY KEY) ENGINE=Aria;
+INSERT INTO t2 VALUES (1),(2),(3);
+CREATE VIEW v2 AS SELECT pk2, COUNT(*) AS cnt FROM t2 GROUP BY pk2;
+SELECT * FROM t1 INNER JOIN v2 ON pk1 = pk2 WHERE f <> 5;
+pk1	f	pk2	cnt
+1	0	1	1
+2	0	2	1
+EXPLAIN EXTENDED SELECT * FROM t1 INNER JOIN v2 ON pk1 = pk2 WHERE f <> 5;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	PRIMARY	t1	ALL	PRIMARY	NULL	NULL	NULL	2	100.00	Using where
+1	PRIMARY	<derived2>	ref	key0	key0	4	test.t1.pk1	2	100.00	
+2	LATERAL DERIVED	t2	eq_ref	PRIMARY	PRIMARY	4	test.t1.pk1	1	100.00	Using index
+Warnings:
+Note	1003	/* select#1 */ select `test`.`t1`.`pk1` AS `pk1`,`test`.`t1`.`f` AS `f`,`v2`.`pk2` AS `pk2`,`v2`.`cnt` AS `cnt` from `test`.`t1` join `test`.`v2` where `v2`.`pk2` = `test`.`t1`.`pk1` and `test`.`t1`.`f` <> 5
+EXPLAIN FORMAT=JSON SELECT * FROM t1 INNER JOIN v2 ON pk1 = pk2 WHERE f <> 5;
+EXPLAIN
+{
+  "query_block": {
+    "select_id": 1,
+    "table": {
+      "table_name": "t1",
+      "access_type": "ALL",
+      "possible_keys": ["PRIMARY"],
+      "rows": 2,
+      "filtered": 100,
+      "attached_condition": "t1.f <> 5"
+    },
+    "table": {
+      "table_name": "<derived2>",
+      "access_type": "ref",
+      "possible_keys": ["key0"],
+      "key": "key0",
+      "key_length": "4",
+      "used_key_parts": ["pk2"],
+      "ref": ["test.t1.pk1"],
+      "rows": 2,
+      "filtered": 100,
+      "materialized": {
+        "query_block": {
+          "select_id": 2,
+          "outer_ref_condition": "t1.pk1 is not null",
+          "table": {
+            "table_name": "t2",
+            "access_type": "eq_ref",
+            "possible_keys": ["PRIMARY"],
+            "key": "PRIMARY",
+            "key_length": "4",
+            "used_key_parts": ["pk2"],
+            "ref": ["test.t1.pk1"],
+            "rows": 1,
+            "filtered": 100,
+            "using_index": true
+          }
+        }
+      }
+    }
+  }
+}
+DROP VIEW v2;
+DROP TABLE t1,t2;

mysql-test/t/derived_cond_pushdown.test

@@ -2535,3 +2535,25 @@ eval $q;
 eval EXPLAIN EXTENDED $q;
 
 DROP TABLE t1;
+
+--echo #
+--echo # MDEV-14880: assertion failure in optimizer when splitting is applied
+--echo #
+
+CREATE TABLE t1 (pk1 INT PRIMARY KEY, f INT) ENGINE=Aria;
+INSERT INTO t1 VALUES (1,0),(2,0);
+
+CREATE TABLE t2 (pk2 INT PRIMARY KEY) ENGINE=Aria;
+INSERT INTO t2 VALUES (1),(2),(3);
+
+CREATE VIEW v2 AS SELECT pk2, COUNT(*) AS cnt FROM t2 GROUP BY pk2;
+
+let $q=
+SELECT * FROM t1 INNER JOIN v2 ON pk1 = pk2 WHERE f <> 5;
+
+eval $q;
+eval EXPLAIN EXTENDED $q;
+eval EXPLAIN FORMAT=JSON $q;
+
+DROP VIEW v2;
+DROP TABLE t1,t2;

sql/opt_split.cc

@@ -922,6 +922,7 @@ SplM_plan_info * JOIN_TAB::choose_best_splitting(double record_count,
     }
     while (keyuse_ext->table == table);
   }
+  spl_opt_info->last_plan= 0;
   if (best_table)
   {
     /*
@@ -963,7 +964,6 @@ SplM_plan_info * JOIN_TAB::choose_best_splitting(double record_count,
       reset_validity_vars_for_keyuses(best_key_keyuse_ext_start, best_table,
                                       best_key, remaining_tables, false);
     }
-    spl_opt_info->last_plan= 0;
     if (spl_plan)
     {
       if(record_count * spl_plan->cost < spl_opt_info->unsplit_cost)