Fixed mdev-15017 Server crashes in in st_join_table::fix_splitting

Do not apply splitting for constant tables.

mysql-test/r/derived_cond_pushdown.result

@@ -14917,3 +14917,14 @@ EXPLAIN
 }
 DROP VIEW v2;
 DROP TABLE t1,t2;
+#
+# MDEV-15017: splittable table is constant table
+#
+CREATE TABLE t1 (a INT) ENGINE=MyISAM;
+CREATE TABLE t2 (pk INT, b INT, PRIMARY KEY (pk)) ENGINE=MyISAM;
+INSERT INTO t2 VALUES (1,2),(3,4);
+CREATE VIEW v2 AS SELECT pk, MIN(b) FROM t2 GROUP BY pk;
+SELECT * FROM t1 LEFT JOIN v2 ON (a = pk);
+a	pk	MIN(b)
+DROP VIEW v2;
+DROP TABLE t1,t2;

mysql-test/t/derived_cond_pushdown.test

@@ -2582,3 +2582,19 @@ eval EXPLAIN FORMAT=JSON $q;
 
 DROP VIEW v2;
 DROP TABLE t1,t2;
+
+--echo #
+--echo # MDEV-15017: splittable table is constant table
+--echo #
+
+CREATE TABLE t1 (a INT) ENGINE=MyISAM;
+
+CREATE TABLE t2 (pk INT, b INT, PRIMARY KEY (pk)) ENGINE=MyISAM;
+INSERT INTO t2 VALUES (1,2),(3,4);
+
+CREATE VIEW v2 AS SELECT pk, MIN(b) FROM t2 GROUP BY pk;
+
+SELECT * FROM t1 LEFT JOIN v2 ON (a = pk);
+
+DROP VIEW v2;
+DROP TABLE t1,t2;

sql/opt_split.cc

@@ -1118,11 +1118,11 @@ bool JOIN::fix_all_splittings_in_plan()
 {
   table_map prev_tables= 0;
   table_map all_tables= (1 << table_count) - 1;
-  for (uint tablenr=0 ; tablenr < table_count ; tablenr++)
+  for (uint tablenr= 0; tablenr < table_count; tablenr++)
   {
     POSITION *cur_pos= &best_positions[tablenr];
     JOIN_TAB *tab= cur_pos->table;
-    if (tab->table->is_splittable())
+    if (tablenr >= const_tables && tab->table->is_splittable())
     {
       SplM_plan_info *spl_plan= cur_pos->spl_plan;
       if (tab->fix_splitting(spl_plan, all_tables & ~prev_tables))

sql/sql_select.cc

@@ -4565,12 +4565,6 @@ make_join_statistics(JOIN *join, List<TABLE_LIST> &tables_list,
     DBUG_EXECUTE("opt", print_keyuse_array(keyuse_array););
   }
 
-  for (s= stat; s < stat_end; s++)
-  {
-    if (s->table->is_splittable())
-      s->add_keyuses_for_splitting();
-  }
-
   join->const_table_map= no_rows_const_tables;
   join->const_tables= const_count;
   eliminate_tables(join);
@@ -4877,6 +4871,9 @@ make_join_statistics(JOIN *join, List<TABLE_LIST> &tables_list,
        s->scan_time();
     }
 
+    if (s->table->is_splittable())
+      s->add_keyuses_for_splitting();
+
     /*
       Set a max range of how many seeks we can expect when using keys
       This is can't be to high as otherwise we are likely to use