From 4feaa06c842b0ae1cc8ab2d6e7f0bbd00c000e87 Mon Sep 17 00:00:00 2001
From: f4rnham <f4rnham@users.noreply.github.com>
Date: Thu, 26 Mar 2015 00:00:12 +0100
Subject: [PATCH] MDEV-7816 ALTER with DROP INDEX and ADD INDEX ..
 COMMENT='comment2' ignores the new comment

Consider two indexes different if their comments differ
---
 mysql-test/r/alter_table.result | 10 ++++++++++
 mysql-test/t/alter_table.test   |  8 ++++++++
 sql/sql_table.cc                |  7 +++++++
 3 files changed, 25 insertions(+)

diff --git a/mysql-test/r/alter_table.result b/mysql-test/r/alter_table.result
index 544e64e6373..a7f8ffcc9ec 100644
--- a/mysql-test/r/alter_table.result
+++ b/mysql-test/r/alter_table.result
@@ -2007,3 +2007,13 @@ INSERT INTO t1 VALUES (1),(2),(3),(4),(5),(6),(7),(8);
 INSERT INTO t1 SELECT a.* FROM t1 a, t1 b, t1 c, t1 d, t1 e;
 ALTER TABLE t1 MODIFY i FLOAT;
 DROP TABLE t1;
+CREATE TABLE t1(a INT);
+CREATE INDEX i1 ON t1(a) COMMENT 'comment1';
+ALTER TABLE t1 DROP INDEX i1, ADD INDEX i1(a) COMMENT 'comment2';
+SHOW CREATE TABLE t1;
+Table	Create Table
+t1	CREATE TABLE `t1` (
+  `a` int(11) DEFAULT NULL,
+  KEY `i1` (`a`) COMMENT 'comment2'
+) ENGINE=MyISAM DEFAULT CHARSET=latin1
+DROP TABLE t1;
diff --git a/mysql-test/t/alter_table.test b/mysql-test/t/alter_table.test
index ab1fb4e4c54..0c0672de3e2 100644
--- a/mysql-test/t/alter_table.test
+++ b/mysql-test/t/alter_table.test
@@ -1697,3 +1697,11 @@ INSERT INTO t1 SELECT a.* FROM t1 a, t1 b, t1 c, t1 d, t1 e;
 ALTER TABLE t1 MODIFY i FLOAT;
 DROP TABLE t1;
 
+#
+# MDEV-7816 ALTER with DROP INDEX and ADD INDEX .. COMMENT='comment2' ignores the new comment
+#
+CREATE TABLE t1(a INT);
+CREATE INDEX i1 ON t1(a) COMMENT 'comment1';
+ALTER TABLE t1 DROP INDEX i1, ADD INDEX i1(a) COMMENT 'comment2';
+SHOW CREATE TABLE t1;
+DROP TABLE t1;
diff --git a/sql/sql_table.cc b/sql/sql_table.cc
index c4b07ad2035..5986e8201c4 100644
--- a/sql/sql_table.cc
+++ b/sql/sql_table.cc
@@ -6368,6 +6368,13 @@ static bool fill_alter_inplace_info(THD *thd,
           new_field->field->field_index != key_part->fieldnr - 1)
         goto index_changed;
     }
+
+    /* Check that key comment is not changed. */
+    if (table_key->comment.length != new_key->comment.length ||
+        (table_key->comment.length &&
+         strcmp(table_key->comment.str, new_key->comment.str) != 0))
+        goto index_changed;
+
     continue;
 
   index_changed: