Merge jamppa@bk-internal.mysql.com:/home/bk/mysql-5.1-new

into  a193-229-222-105.elisa-laajakaista.fi:/home/my/bk/mysql-5.1-new

mysql-test/r/alter_table.result

@@ -647,3 +647,13 @@ SELECT LENGTH(s) FROM t1;
 LENGTH(s)
 10
 DROP TABLE t1;
+CREATE TABLE t1 (v VARCHAR(3), b INT);
+INSERT INTO t1 VALUES ('abc', 5);
+SELECT * FROM t1;
+v	b
+abc	5
+ALTER TABLE t1 MODIFY COLUMN v VARCHAR(4);
+SELECT * FROM t1;
+v	b
+abc	5
+DROP TABLE t1;

mysql-test/t/alter_table.test

@@ -469,3 +469,16 @@ ALTER TABLE t1 MODIFY s BINARY(10);
 SELECT HEX(s) FROM t1;
 SELECT LENGTH(s) FROM t1;
 DROP TABLE t1;
+
+#
+# Bug#19386: Multiple alter causes crashed table
+# The trailing column would get corrupted data, or server could not even read
+# it.
+#
+
+CREATE TABLE t1 (v VARCHAR(3), b INT);
+INSERT INTO t1 VALUES ('abc', 5);
+SELECT * FROM t1;
+ALTER TABLE t1 MODIFY COLUMN v VARCHAR(4);
+SELECT * FROM t1;
+DROP TABLE t1;

sql/ha_myisam.cc

@@ -1786,7 +1786,8 @@ bool ha_myisam::check_if_incompatible_data(HA_CREATE_INFO *info,
   if (info->auto_increment_value != auto_increment_value ||
       info->data_file_name != data_file_name ||
       info->index_file_name != index_file_name ||
-      table_changes == IS_EQUAL_NO)
+      table_changes == IS_EQUAL_NO ||
+      table_changes & IS_EQUAL_PACK_LENGTH) // Not implemented yet
     return COMPATIBLE_DATA_NO;
 
   if ((options & (HA_OPTION_PACK_RECORD | HA_OPTION_CHECKSUM |