Change create_field->offset to store offset from start of fields, independent of null bits.

Count null_bits separately from field offsets and adjust them in case of primary key parts.
(Previously a CREATE TABLE with a lot of null fields that was part of a primary key caused MySQL to wrongly count the number of bytes needed to store null bits)
This is a more complete bug fix for #6236


mysql-test/r/alter_table.result:
  More test for bug #6236 (CREATE TABLE didn't properly count not null columns for primary keys)
mysql-test/t/alter_table.test:
  More test for bug #6236 (CREATE TABLE didn't properly count not null columns for primary keys)
sql/handler.h:
  Add counter for null fields
sql/sql_table.cc:
  Change create_field->offset to store offset from start of fields, independent of null bits.
  Count null_bits separately from field offsets and adjust them in case of primary key parts.
sql/unireg.cc:
  Change create_field->offset to store offset from start of fields, independent of null bits.
  Count null_bits separately from field offsets and adjust them in case of primary key parts.

2 files changed, 33 insertions, 0 deletions

diff --git a/mysql-test/r/alter_table.result b/mysql-test/r/alter_table.result
index 80d3ef5e0a5..19d2ca4d6ed 100644
--- a/mysql-test/r/alter_table.result
+++ b/mysql-test/r/alter_table.result
@@ -406,3 +406,19 @@ t2	CREATE TABLE `t2` (
   PRIMARY KEY  (`a`)
 ) TYPE=MRG_MyISAM UNION=(t1)
 drop table if exists t1, t2;
+create table t1 (a int, b int, c int, d int, e int, f int, g int, h int,i int, primary key (a,b,c,d,e,f,g,i,h)) engine=MyISAM;
+insert into t1 (a) values(1);
+show table status like 't1';
+Name	Type	Row_format	Rows	Avg_row_length	Data_length	Max_data_length	Index_length	Data_free	Auto_increment	Create_time	Update_time	Check_time	Create_options	Comment
+t1	MyISAM	Fixed	1	37	37	X	X	X	X	X	X	X	X	
+alter table t1 modify a int;
+show table status like 't1';
+Name	Type	Row_format	Rows	Avg_row_length	Data_length	Max_data_length	Index_length	Data_free	Auto_increment	Create_time	Update_time	Check_time	Create_options	Comment
+t1	MyISAM	Fixed	1	37	37	X	X	X	X	X	X	X	X	
+drop table t1;
+create table t1 (a int not null, b int not null, c int not null, d int not null, e int not null, f int not null, g int not null, h int not null,i int not null, primary key (a,b,c,d,e,f,g,i,h)) engine=MyISAM;
+insert into t1 (a) values(1);
+show table status like 't1';
+Name	Type	Row_format	Rows	Avg_row_length	Data_length	Max_data_length	Index_length	Data_free	Auto_increment	Create_time	Update_time	Check_time	Create_options	Comment
+t1	MyISAM	Fixed	1	37	37	X	X	X	X	X	X	X	X	
+drop table t1;
diff --git a/mysql-test/t/alter_table.test b/mysql-test/t/alter_table.test
index c69f9aabae6..af0ec2bca16 100644
--- a/mysql-test/t/alter_table.test
+++ b/mysql-test/t/alter_table.test
@@ -267,3 +267,20 @@ flush tables;
 alter table t1 modify a varchar(10) not null;
 show create table t2;
 drop table if exists t1, t2;
+
+# The following is also part of bug #6236 (CREATE TABLE didn't properly count
+# not null columns for primary keys)
+
+create table t1 (a int, b int, c int, d int, e int, f int, g int, h int,i int, primary key (a,b,c,d,e,f,g,i,h)) engine=MyISAM;
+insert into t1 (a) values(1);
+--replace_column 7 X 8 X 9 X 10 X 11 X 12 X 13 X 14 X
+show table status like 't1';
+alter table t1 modify a int;
+--replace_column 7 X 8 X 9 X 10 X 11 X 12 X 13 X 14 X
+show table status like 't1';
+drop table t1;
+create table t1 (a int not null, b int not null, c int not null, d int not null, e int not null, f int not null, g int not null, h int not null,i int not null, primary key (a,b,c,d,e,f,g,i,h)) engine=MyISAM;
+insert into t1 (a) values(1);
+--replace_column 7 X 8 X 9 X 10 X 11 X 12 X 13 X 14 X
+show table status like 't1';
+drop table t1;