Fixed MDEV-14994 Assertion `join->best_read < double(1.79...15e+308L)' or

server crash in JOIN::fix_all_splittings_in_plan

Cost formulas must take into account the case when a splittable table
has now rows.

mysql-test/r/derived_cond_pushdown.result

@@ -14928,3 +14928,20 @@ SELECT * FROM t1 LEFT JOIN v2 ON (a = pk);
 a	pk	MIN(b)
 DROP VIEW v2;
 DROP TABLE t1,t2;
+#
+# MDEV-14994: splittable table with no rows
+#
+CREATE TABLE t1 (f INT PRIMARY KEY) ENGINE=MyISAM;
+CREATE VIEW v1 AS SELECT a.* FROM t1 AS a STRAIGHT_JOIN t1 AS b;
+CREATE VIEW v2 AS SELECT f FROM v1 GROUP BY f;
+SELECT * FROM v1 JOIN v2 ON v1.f = v2.f;
+f	f
+EXPLAIN EXTENDED
+SELECT * FROM v1 JOIN v2 ON v1.f = v2.f;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	PRIMARY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE noticed after reading const tables
+3	LATERAL DERIVED	NULL	NULL	NULL	NULL	NULL	NULL	NULL	NULL	no matching row in const table
+Warnings:
+Note	1003	/* select#1 */ select NULL AS `f`,`v2`.`f` AS `f` from `test`.`t1` `a` straight_join `test`.`t1` `b` join `test`.`v2` where 0
+DROP VIEW v1,v2;
+DROP TABLE t1;

mysql-test/t/derived_cond_pushdown.test

@@ -2598,3 +2598,18 @@ SELECT * FROM t1 LEFT JOIN v2 ON (a = pk);
 
 DROP VIEW v2;
 DROP TABLE t1,t2;
+
+--echo #
+--echo # MDEV-14994: splittable table with no rows
+--echo #
+
+CREATE TABLE t1 (f INT PRIMARY KEY) ENGINE=MyISAM;
+CREATE VIEW v1 AS SELECT a.* FROM t1 AS a STRAIGHT_JOIN t1 AS b;
+CREATE VIEW v2 AS SELECT f FROM v1 GROUP BY f;
+
+SELECT * FROM v1 JOIN v2 ON v1.f = v2.f;
+EXPLAIN EXTENDED
+SELECT * FROM v1 JOIN v2 ON v1.f = v2.f;
+
+DROP VIEW v1,v2;
+DROP TABLE t1;

sql/opt_split.cc

@@ -645,7 +645,8 @@ double spl_postjoin_oper_cost(THD *thd, double join_record_count, uint rec_len)
   cost+= get_tmp_table_lookup_cost(thd, join_record_count,rec_len) *
          join_record_count;   // cost to perform post join operation used here
   cost+= get_tmp_table_lookup_cost(thd, join_record_count, rec_len) +
-         join_record_count * log2 (join_record_count) *
+         (join_record_count == 0 ? 0 :
+          join_record_count * log2 (join_record_count)) *
          SORT_INDEX_CMP_COST;             // cost to perform  sorting
   return cost;
 }
@@ -948,7 +949,9 @@ SplM_plan_info * JOIN_TAB::choose_best_splitting(double record_count,
       spl_plan->table= best_table;
       spl_plan->key= best_key;
       spl_plan->parts= best_key_parts;
-      spl_plan->split_sel= best_rec_per_key / spl_opt_info->unsplit_card;
+      spl_plan->split_sel= best_rec_per_key /
+                           (spl_opt_info->unsplit_card ?
+                            spl_opt_info->unsplit_card : 1); 
 
       uint rec_len= table->s->rec_buff_length;