Bug#31399 Wrong query result when doing join buffering over BIT fields

if table has bit fields then uneven bits(if exist) are stored into null bits place.
So we need to copy null bits in case of uneven bit field presence.

mysql-test/r/type_bit.result

@@ -723,4 +723,30 @@ CREATE TABLE IF NOT EXISTS t1 (
 f1 bit(2) NOT NULL default b''
 ) ENGINE=MyISAM DEFAULT CHARSET=latin1 COLLATE=latin1_general_ci;
 ERROR 42000: Invalid default value for 'f1'
+create table t1bit7 (a1 bit(7) not null) engine=MyISAM;
+create table t2bit7 (b1 bit(7)) engine=MyISAM;
+insert into t1bit7 values (b'1100000');
+insert into t1bit7 values (b'1100001');
+insert into t1bit7 values (b'1100010');
+insert into t2bit7 values (b'1100001');
+insert into t2bit7 values (b'1100010');
+insert into t2bit7 values (b'1100110');
+select bin(a1) from t1bit7, t2bit7 where t1bit7.a1=t2bit7.b1;
+bin(a1)
+1100001
+1100010
+drop table t1bit7, t2bit7;
+create table t1bit7 (a1 bit(15) not null) engine=MyISAM;
+create table t2bit7 (b1 bit(15)) engine=MyISAM;
+insert into t1bit7 values (b'110000011111111');
+insert into t1bit7 values (b'110000111111111');
+insert into t1bit7 values (b'110001011111111');
+insert into t2bit7 values (b'110000111111111');
+insert into t2bit7 values (b'110001011111111');
+insert into t2bit7 values (b'110011011111111');
+select bin(a1) from t1bit7, t2bit7 where t1bit7.a1=t2bit7.b1;
+bin(a1)
+110000111111111
+110001011111111
+drop table t1bit7, t2bit7;
 End of 5.0 tests

mysql-test/t/type_bit.test

@@ -367,4 +367,34 @@ CREATE TABLE IF NOT EXISTS t1 (
 f1 bit(2) NOT NULL default b''
 ) ENGINE=MyISAM DEFAULT CHARSET=latin1 COLLATE=latin1_general_ci;
 
+
+#
+# Bug#31399 Wrong query result when doing join buffering over BIT fields 
+#
+create table t1bit7 (a1 bit(7) not null) engine=MyISAM; 
+create table t2bit7 (b1 bit(7)) engine=MyISAM; 
+
+insert into t1bit7 values (b'1100000'); 
+insert into t1bit7 values (b'1100001'); 
+insert into t1bit7 values (b'1100010'); 
+insert into t2bit7 values (b'1100001'); 
+insert into t2bit7 values (b'1100010'); 
+insert into t2bit7 values (b'1100110'); 
+
+select bin(a1) from t1bit7, t2bit7 where t1bit7.a1=t2bit7.b1; 
+drop table t1bit7, t2bit7; 
+
+create table t1bit7 (a1 bit(15) not null) engine=MyISAM; 
+create table t2bit7 (b1 bit(15)) engine=MyISAM; 
+
+insert into t1bit7 values (b'110000011111111'); 
+insert into t1bit7 values (b'110000111111111'); 
+insert into t1bit7 values (b'110001011111111'); 
+insert into t2bit7 values (b'110000111111111'); 
+insert into t2bit7 values (b'110001011111111'); 
+insert into t2bit7 values (b'110011011111111'); 
+
+select bin(a1) from t1bit7, t2bit7 where t1bit7.a1=t2bit7.b1; 
+drop table t1bit7, t2bit7; 
+
 --echo End of 5.0 tests

sql/sql_select.cc

@@ -13233,6 +13233,7 @@ join_init_cache(THD *thd,JOIN_TAB *tables,uint table_count)
   length=0;
   for (i=0 ; i < table_count ; i++)
   {
+    bool have_bit_fields= FALSE;
     uint null_fields=0,used_fields;
 
     Field **f_ptr,*field;
@@ -13247,13 +13248,16 @@ join_init_cache(THD *thd,JOIN_TAB *tables,uint table_count)
 	length+=field->fill_cache_field(copy);
 	if (copy->blob_field)
 	  (*blob_ptr++)=copy;
-	if (field->maybe_null())
+	if (field->real_maybe_null())
 	  null_fields++;
+        if (field->type() == MYSQL_TYPE_BIT &&
+            ((Field_bit*)field)->bit_len)
+          have_bit_fields= TRUE;    
 	copy++;
       }
     }
     /* Copy null bits from table */
-    if (null_fields && tables[i].table->s->null_fields)
+    if (null_fields || have_bit_fields)
     {						/* must copy null bits */
       copy->str=(char*) tables[i].table->null_flags;
       copy->length= tables[i].table->s->null_bytes;