Fixed LP bug #675922.

The bug happened when BKA join algorithm used an incremental buffer
and some of the fields over which access keys were constructed
- were allocated in the previous join buffers
- were non-nullable
- belonged to inner tables of outer joins.
For such fields an offset to the field value in the record is saved
in the postfix of the record, and a zero offset indicates that the value 
is null. Before the key using the field value is constructed the
value is read into the corresponding field of the record buffer and
the null bit is set for the field if the offset is 0. However if
the field is non-nullable the table->null_row must be set to 1
for null values and to 0 for non-null values  to ensure proper reading
of the value from the record buffer.

3 files changed, 113 insertions, 3 deletions

diff --git a/mysql-test/r/join_cache.result b/mysql-test/r/join_cache.result
index 36152af7898..4973288cd9f 100644
--- a/mysql-test/r/join_cache.result
+++ b/mysql-test/r/join_cache.result
@@ -6004,4 +6004,56 @@ a1	a2	b2	a3	b3
 SET SESSION optimizer_switch = 'outer_join_with_cache=off';
 SET SESSION join_cache_level = DEFAULT;
 DROP TABLE t1,t2,t3;
+#
+# Bug #675922: incremental buffer for BKA with access from previous
+#      buffers from non-nullable columns whose values may be null
+#
+CREATE TABLE t1 (a1 varchar(32)) ;
+INSERT INTO t1 VALUES ('s'),('k');
+CREATE TABLE t2 (a2 int PRIMARY KEY, b2 varchar(32)) ;
+INSERT INTO t2 VALUES (7,'s');
+CREATE TABLE t3 (a3 int PRIMARY KEY, b3 varchar(32)) ;
+INSERT INTO t3 VALUES (7,'s');
+CREATE TABLE t4 (a4 int) ;
+INSERT INTO t4 VALUES (9);
+CREATE TABLE t5(a5 int PRIMARY KEY, b5 int) ;
+INSERT INTO t5 VALUES (7,0);
+SET SESSION optimizer_switch = 'outer_join_with_cache=on';
+SET SESSION join_cache_level = 0;
+EXPLAIN
+SELECT t4.a4, t5.b5 
+FROM ((t1 LEFT JOIN (t2 JOIN t3 ON t2.a2 = t3.a3) ON t2.b2 = t1.a1)
+LEFT JOIN t4 ON t4.a4 <> 0) LEFT JOIN t5 ON t5.a5 = t2.a2;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	2	
+1	SIMPLE	t2	ALL	PRIMARY	NULL	NULL	NULL	1	Using where
+1	SIMPLE	t3	eq_ref	PRIMARY	PRIMARY	4	test.t2.a2	1	Using index
+1	SIMPLE	t4	ALL	NULL	NULL	NULL	NULL	1	Using where
+1	SIMPLE	t5	eq_ref	PRIMARY	PRIMARY	4	test.t2.a2	1	Using where
+SELECT t4.a4, t5.b5 
+FROM ((t1 LEFT JOIN (t2 JOIN t3 ON t2.a2 = t3.a3) ON t2.b2 = t1.a1)
+LEFT JOIN t4 ON t4.a4 <> 0) LEFT JOIN t5 ON t5.a5 = t2.a2;
+a4	b5
+9	0
+9	NULL
+SET SESSION join_cache_level = 6;
+EXPLAIN
+SELECT t4.a4, t5.b5 
+FROM ((t1 LEFT JOIN (t2 JOIN t3 ON t2.a2 = t3.a3) ON t2.b2 = t1.a1)
+LEFT JOIN t4 ON t4.a4 <> 0) LEFT JOIN t5 ON t5.a5 = t2.a2;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	2	
+1	SIMPLE	t2	ALL	PRIMARY	NULL	NULL	NULL	1	Using where
+1	SIMPLE	t3	eq_ref	PRIMARY	PRIMARY	4	test.t2.a2	1	Using index
+1	SIMPLE	t4	ALL	NULL	NULL	NULL	NULL	1	Using where; Using join buffer (flat, BNL join)
+1	SIMPLE	t5	eq_ref	PRIMARY	PRIMARY	4	test.t2.a2	1	Using where; Using join buffer (incremental, BKA join)
+SELECT t4.a4, t5.b5 
+FROM ((t1 LEFT JOIN (t2 JOIN t3 ON t2.a2 = t3.a3) ON t2.b2 = t1.a1)
+LEFT JOIN t4 ON t4.a4 <> 0) LEFT JOIN t5 ON t5.a5 = t2.a2;
+a4	b5
+9	0
+9	NULL
+SET SESSION optimizer_switch = 'outer_join_with_cache=off';
+SET SESSION join_cache_level = DEFAULT;
+DROP TABLE t1,t2,t3,t4,t5;
 set @@optimizer_switch=@save_optimizer_switch;
diff --git a/mysql-test/t/join_cache.test b/mysql-test/t/join_cache.test
index bb0d1b56a3d..1905297b25b 100644
--- a/mysql-test/t/join_cache.test
+++ b/mysql-test/t/join_cache.test
@@ -2655,5 +2655,50 @@ SET SESSION join_cache_level = DEFAULT;
 
 DROP TABLE t1,t2,t3;
 
+--echo #
+--echo # Bug #675922: incremental buffer for BKA with access from previous
+--echo #      buffers from non-nullable columns whose values may be null
+--echo #
+
+CREATE TABLE t1 (a1 varchar(32)) ;
+INSERT INTO t1 VALUES ('s'),('k');
+
+CREATE TABLE t2 (a2 int PRIMARY KEY, b2 varchar(32)) ;
+INSERT INTO t2 VALUES (7,'s');
+
+CREATE TABLE t3 (a3 int PRIMARY KEY, b3 varchar(32)) ;
+INSERT INTO t3 VALUES (7,'s');
+
+CREATE TABLE t4 (a4 int) ;
+INSERT INTO t4 VALUES (9);
+
+CREATE TABLE t5(a5 int PRIMARY KEY, b5 int) ;
+INSERT INTO t5 VALUES (7,0);
+
+SET SESSION optimizer_switch = 'outer_join_with_cache=on';
+
+SET SESSION join_cache_level = 0;
+EXPLAIN
+SELECT t4.a4, t5.b5 
+  FROM ((t1 LEFT JOIN (t2 JOIN t3 ON t2.a2 = t3.a3) ON t2.b2 = t1.a1)
+       LEFT JOIN t4 ON t4.a4 <> 0) LEFT JOIN t5 ON t5.a5 = t2.a2;
+SELECT t4.a4, t5.b5 
+  FROM ((t1 LEFT JOIN (t2 JOIN t3 ON t2.a2 = t3.a3) ON t2.b2 = t1.a1)
+       LEFT JOIN t4 ON t4.a4 <> 0) LEFT JOIN t5 ON t5.a5 = t2.a2;
+
+SET SESSION join_cache_level = 6;
+EXPLAIN
+SELECT t4.a4, t5.b5 
+  FROM ((t1 LEFT JOIN (t2 JOIN t3 ON t2.a2 = t3.a3) ON t2.b2 = t1.a1)
+       LEFT JOIN t4 ON t4.a4 <> 0) LEFT JOIN t5 ON t5.a5 = t2.a2;
+SELECT t4.a4, t5.b5 
+  FROM ((t1 LEFT JOIN (t2 JOIN t3 ON t2.a2 = t3.a3) ON t2.b2 = t1.a1)
+       LEFT JOIN t4 ON t4.a4 <> 0) LEFT JOIN t5 ON t5.a5 = t2.a2;
+
+SET SESSION optimizer_switch = 'outer_join_with_cache=off';
+SET SESSION join_cache_level = DEFAULT;
+
+DROP TABLE t1,t2,t3,t4,t5;
+
 # this must be the last command in the file
 set @@optimizer_switch=@save_optimizer_switch;
diff --git a/sql/sql_join_cache.cc b/sql/sql_join_cache.cc
index c3f2dfa5541..713d6f9e93f 100644
--- a/sql/sql_join_cache.cc
+++ b/sql/sql_join_cache.cc
@@ -1776,7 +1776,13 @@ uint JOIN_CACHE::read_record_field(CACHE_FIELD *copy, bool blob_in_rec_buff)
     If the value of *len is 0 then the function sets it to the total
     length of the record fields including possible trailing offset
     values. Otherwise *len is supposed to provide this value that
-    has been obtained earlier.  
+    has been obtained earlier. 
+
+  NOTE
+    If the value of the referenced field is null then the offset
+    for the value is set to 0. If the value of a field can be null
+    then the value of flag_fields is always positive. So the offset
+    for any non-null value cannot be 0 in this case. 
 
   RETURN VALUE
     TRUE   'copy' points to a data descriptor of this join cache
@@ -1805,14 +1811,21 @@ bool JOIN_CACHE::read_referenced_field(CACHE_FIELD *copy,
                          size_of_fld_ofs*
                          (referenced_fields+1-copy->referenced_field_no));  
   bool is_null= FALSE;
+  Field *field= copy->field;
   if (offset == 0 && flag_fields)
     is_null= TRUE;
   if (is_null)
-    copy->field->set_null();
+  {
+    field->set_null();
+    if (!field->real_maybe_null())
+      field->table->null_row= 1;
+  }
   else
   {
     uchar *save_pos= pos;
-    copy->field->set_notnull(); 
+    field->set_notnull(); 
+    if (!field->real_maybe_null())
+      field->table->null_row= 0;
     pos= rec_ptr+offset;
     read_record_field(copy, blob_data_is_in_rec_buff(rec_ptr));
     pos= save_pos;