Fixed LP bug #901709.

The cause of the reported assertion failure was a division of a double value by 0. 

mysql-test/r/subselect_sj.result

@@ -2118,4 +2118,35 @@ a	b
 1	1
 set optimizer_switch= @tmp_otimizer_switch;
 DROP TABLE t1,t2,t3;
+#
+# Bug #901709: assertion failure with record count == 0 
+#
+CREATE TABLE t1 (a int, KEY (a));
+INSERT INTO t1 VALUES (4), (6);
+CREATE TABLE t2 (a int, KEY (a));
+INSERT INTO t2 VALUES (4), (6);
+CREATE TABLE t3 (b int);
+INSERT INTO t3 VALUES (4);
+CREATE TABLE t4 (c int);
+SET @tmp_optimizer_switch=@@optimizer_switch;
+SET @@optimizer_switch='semijoin=on';
+SET @@optimizer_switch='materialization=on';
+SET @@optimizer_switch='firstmatch=on';
+SET optimizer_switch='semijoin_with_cache=on';
+SET optimizer_prune_level=0;
+EXPLAIN
+SELECT * FROM t1, t2
+WHERE t1.a = t2.a AND t2.a IN (SELECT b FROM t3 STRAIGHT_JOIN t4);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t3	system	NULL	NULL	NULL	NULL	1	
+1	PRIMARY	<subquery2>	ALL	distinct_key	NULL	NULL	NULL	1	
+1	PRIMARY	t1	ref	a	a	5	const	1	Using index
+1	PRIMARY	t2	ref	a	a	5	test.t3.b	1	Using index
+2	MATERIALIZED	t4	ALL	NULL	NULL	NULL	NULL	0	
+SELECT * FROM t1, t2
+WHERE t1.a = t2.a AND t2.a IN (SELECT b FROM t3 STRAIGHT_JOIN t4);
+a	a
+SET optimizer_prune_level=DEFAULT;
+SET optimizer_switch=@tmp_optimizer_switch;
+DROP TABLE t1,t2,t3,t4;
 set optimizer_switch=@subselect_sj_tmp;

mysql-test/r/subselect_sj_jcl6.result

@@ -2124,6 +2124,37 @@ a	b
 1	1
 set optimizer_switch= @tmp_otimizer_switch;
 DROP TABLE t1,t2,t3;
+#
+# Bug #901709: assertion failure with record count == 0 
+#
+CREATE TABLE t1 (a int, KEY (a));
+INSERT INTO t1 VALUES (4), (6);
+CREATE TABLE t2 (a int, KEY (a));
+INSERT INTO t2 VALUES (4), (6);
+CREATE TABLE t3 (b int);
+INSERT INTO t3 VALUES (4);
+CREATE TABLE t4 (c int);
+SET @tmp_optimizer_switch=@@optimizer_switch;
+SET @@optimizer_switch='semijoin=on';
+SET @@optimizer_switch='materialization=on';
+SET @@optimizer_switch='firstmatch=on';
+SET optimizer_switch='semijoin_with_cache=on';
+SET optimizer_prune_level=0;
+EXPLAIN
+SELECT * FROM t1, t2
+WHERE t1.a = t2.a AND t2.a IN (SELECT b FROM t3 STRAIGHT_JOIN t4);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t3	system	NULL	NULL	NULL	NULL	1	
+1	PRIMARY	<subquery2>	ALL	distinct_key	NULL	NULL	NULL	1	
+1	PRIMARY	t1	ref	a	a	5	const	1	Using index
+1	PRIMARY	t2	ref	a	a	5	test.t3.b	1	Using index
+2	MATERIALIZED	t4	ALL	NULL	NULL	NULL	NULL	0	
+SELECT * FROM t1, t2
+WHERE t1.a = t2.a AND t2.a IN (SELECT b FROM t3 STRAIGHT_JOIN t4);
+a	a
+SET optimizer_prune_level=DEFAULT;
+SET optimizer_switch=@tmp_optimizer_switch;
+DROP TABLE t1,t2,t3,t4;
 set optimizer_switch=@subselect_sj_tmp;
 #
 # BUG#49129: Wrong result with IN-subquery with join_cache_level=6 and firstmatch=off

mysql-test/t/subselect_sj.test

@@ -1937,5 +1937,35 @@ set optimizer_switch= @tmp_otimizer_switch;
 
 DROP TABLE t1,t2,t3;
 
+--echo #
+--echo # Bug #901709: assertion failure with record count == 0 
+--echo #
+
+CREATE TABLE t1 (a int, KEY (a));
+INSERT INTO t1 VALUES (4), (6);
+CREATE TABLE t2 (a int, KEY (a));
+INSERT INTO t2 VALUES (4), (6);
+CREATE TABLE t3 (b int);
+INSERT INTO t3 VALUES (4);
+CREATE TABLE t4 (c int);
+
+SET @tmp_optimizer_switch=@@optimizer_switch;
+SET @@optimizer_switch='semijoin=on';
+SET @@optimizer_switch='materialization=on';
+SET @@optimizer_switch='firstmatch=on';
+SET optimizer_switch='semijoin_with_cache=on';
+SET optimizer_prune_level=0;
+
+EXPLAIN
+SELECT * FROM t1, t2
+ WHERE t1.a = t2.a AND t2.a IN (SELECT b FROM t3 STRAIGHT_JOIN t4);
+SELECT * FROM t1, t2
+ WHERE t1.a = t2.a AND t2.a IN (SELECT b FROM t3 STRAIGHT_JOIN t4);
+
+SET optimizer_prune_level=DEFAULT;
+SET optimizer_switch=@tmp_optimizer_switch;
+
+DROP TABLE t1,t2,t3,t4;
+
 # The following command must be the last one the file 
 set optimizer_switch=@subselect_sj_tmp;

sql/opt_subselect.cc

@@ -2629,6 +2629,7 @@ bool Firstmatch_picker::check_qep(JOIN *join,
              - read_time is the same (i.e. FirstMatch doesn't add any cost
              - remove fanout added by the last table
           */
+          if (*record_count)
             *record_count /= join->positions[idx].records_read;
         }
         else