Merged fix for bug #12652385 - "61493: REORDERING COLUMNS

TO POSITION FIRST CAN CAUSE DATA TO BE CORRUPTED" into
mysql-5.5 tree.

mysql-test/r/alter_table.result

@@ -1345,6 +1345,35 @@ DROP TABLE t1;
 CREATE TABLE t1 (a TEXT, id INT, b INT);
 ALTER TABLE t1 DROP COLUMN a, ADD COLUMN c TEXT FIRST;
 DROP TABLE t1;
+#
+# Test for bug #12652385 - "61493: REORDERING COLUMNS TO POSITION
+#                           FIRST CAN CAUSE DATA TO BE CORRUPTED".
+#
+drop table if exists t1;
+# Use MyISAM engine as the fact that InnoDB doesn't support
+# in-place ALTER TABLE in cases when columns are being renamed
+# hides some bugs.
+create table t1 (i int, j int) engine=myisam;
+insert into t1 value (1, 2);
+# First, test for original problem described in the bug report.
+select * from t1;
+i	j
+1	2
+# Change of column order by the below ALTER TABLE statement should
+# affect both column names and column contents.
+alter table t1 modify column j int first;
+select * from t1;
+j	i
+2	1
+# Now test for similar problem with the same root.
+# The below ALTER TABLE should change not only the name but
+# also the value for the last column of the table.
+alter table t1 drop column i, add column k int default 0;
+select * from t1;
+j	k
+2	0
+# Clean-up.
+drop table t1;
 End of 5.1 tests
 CREATE TABLE t1(c CHAR(10), 
 i INT UNSIGNED AUTO_INCREMENT NOT NULL PRIMARY KEY);

mysql-test/t/alter_table.test

@@ -1073,6 +1073,33 @@ ALTER TABLE t1 DROP COLUMN a, ADD COLUMN c TEXT FIRST;
 DROP TABLE t1;
 
 
+--echo #
+--echo # Test for bug #12652385 - "61493: REORDERING COLUMNS TO POSITION
+--echo #                           FIRST CAN CAUSE DATA TO BE CORRUPTED".
+--echo #
+--disable_warnings
+drop table if exists t1;
+--enable_warnings
+--echo # Use MyISAM engine as the fact that InnoDB doesn't support
+--echo # in-place ALTER TABLE in cases when columns are being renamed
+--echo # hides some bugs.
+create table t1 (i int, j int) engine=myisam;
+insert into t1 value (1, 2);
+--echo # First, test for original problem described in the bug report.
+select * from t1;
+--echo # Change of column order by the below ALTER TABLE statement should
+--echo # affect both column names and column contents.
+alter table t1 modify column j int first;
+select * from t1;
+--echo # Now test for similar problem with the same root.
+--echo # The below ALTER TABLE should change not only the name but
+--echo # also the value for the last column of the table.
+alter table t1 drop column i, add column k int default 0;
+select * from t1;
+--echo # Clean-up.
+drop table t1;
+
+
 --echo End of 5.1 tests
 
 #

sql/sql_table.cc

@@ -5326,6 +5326,12 @@ mysql_prepare_alter_table(THD *thd, TABLE *table,
     if (drop)
     {
       drop_it.remove();
+      /*
+        ALTER TABLE DROP COLUMN always changes table data even in cases
+        when new version of the table has the same structure as the old
+        one.
+      */
+      alter_info->change_level= ALTER_TABLE_DATA_CHANGED;
       continue;
     }
     /* Check if field is changed */
@@ -5403,7 +5409,14 @@ mysql_prepare_alter_table(THD *thd, TABLE *table,
     if (!def->after)
       new_create_list.push_back(def);
     else if (def->after == first_keyword)
+    {
       new_create_list.push_front(def);
+      /*
+        Re-ordering columns in table can't be done using in-place algorithm
+        as it always changes table data.
+      */
+      alter_info->change_level= ALTER_TABLE_DATA_CHANGED;
+    }
     else
     {
       Create_field *find;
@@ -5419,6 +5432,10 @@ mysql_prepare_alter_table(THD *thd, TABLE *table,
         goto err;
       }
       find_it.after(def);			// Put element after this
+      /*
+        Re-ordering columns in table can't be done using in-place algorithm
+        as it always changes table data.
+      */
       alter_info->change_level= ALTER_TABLE_DATA_CHANGED;
     }
   }