From a21a0b47ca46212a528c4402e4b473fe51437422 Mon Sep 17 00:00:00 2001
From: Georgi Kodinov <joro@sun.com>
Date: Fri, 18 Dec 2009 14:00:30 +0200
Subject: [PATCH] Bug #31145: ALTER TABLE DROP COLUMN, ADD COLUMN crashes
 (linux) or   freezes (win) the server

The check for equality was assuming the field object is always
created. If it's not it was de-referencing a NULL pointer.
Fixed to use the data in the create object instead.
---
 mysql-test/r/alter_table.result |  7 +++++++
 mysql-test/t/alter_table.test   | 12 ++++++++++++
 sql/field.cc                    |  3 +--
 3 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/mysql-test/r/alter_table.result b/mysql-test/r/alter_table.result
index 06f4e7fbe8a..004e2031fb1 100644
--- a/mysql-test/r/alter_table.result
+++ b/mysql-test/r/alter_table.result
@@ -1338,4 +1338,11 @@ ALTER TABLE t1 CHANGE COLUMN f1 f1_no_real_change TIMESTAMP NULL DEFAULT NULL;
 affected rows: 0
 info: Records: 0  Duplicates: 0  Warnings: 0
 DROP TABLE t1;
+#
+# Bug #31145: ALTER TABLE DROP COLUMN, ADD COLUMN crashes (linux) 
+#   or freezes (win) the server
+#
+CREATE TABLE t1 (a TEXT, id INT, b INT);
+ALTER TABLE t1 DROP COLUMN a, ADD COLUMN c TEXT FIRST;
+DROP TABLE t1;
 End of 5.1 tests
diff --git a/mysql-test/t/alter_table.test b/mysql-test/t/alter_table.test
index 5534aa0a234..4989a6c380c 100644
--- a/mysql-test/t/alter_table.test
+++ b/mysql-test/t/alter_table.test
@@ -1061,4 +1061,16 @@ ALTER TABLE t1 CHANGE COLUMN f1 f1_no_real_change TIMESTAMP NULL DEFAULT NULL;
 --disable_info
 DROP TABLE t1;
 
+
+--echo #
+--echo # Bug #31145: ALTER TABLE DROP COLUMN, ADD COLUMN crashes (linux) 
+--echo #   or freezes (win) the server
+--echo #
+
+CREATE TABLE t1 (a TEXT, id INT, b INT);
+ALTER TABLE t1 DROP COLUMN a, ADD COLUMN c TEXT FIRST;
+
+DROP TABLE t1;
+
+
 --echo End of 5.1 tests
diff --git a/sql/field.cc b/sql/field.cc
index 01ccc338782..d8db3fdbae4 100644
--- a/sql/field.cc
+++ b/sql/field.cc
@@ -8282,8 +8282,7 @@ uint Field_blob::is_equal(Create_field *new_field)
 
   return ((new_field->sql_type == get_blob_type_from_length(max_data_length()))
           && new_field->charset == field_charset &&
-          ((Field_blob *)new_field->field)->max_data_length() ==
-          max_data_length());
+          new_field->pack_length == pack_length());
 }