Fix for bug#23113: Different behavior on altering ENUM fields between 5.0 and 5.1

Problem: mysqld doesn't detect that enum data must be reinserted performing
'ALTER TABLE' in some cases.

Fix: reinsert data altering an enum field if enum values are changed.

mysql-test/r/alter_table.result

@@ -1222,4 +1222,16 @@ ALTER TABLE t1 CHANGE d c varchar(10);
 affected rows: 0
 info: Records: 0  Duplicates: 0  Warnings: 0
 DROP TABLE t1;
+CREATE TABLE t1(a INT AUTO_INCREMENT PRIMARY KEY, 
+b ENUM('a', 'b', 'c') NOT NULL);
+INSERT INTO t1 (b) VALUES ('a'), ('c'), ('b'), ('b'), ('a');
+ALTER TABLE t1 MODIFY b ENUM('a', 'z', 'b', 'c') NOT NULL;
+SELECT * FROM t1;
+a	b
+1	a
+2	c
+3	b
+4	b
+5	a
+DROP TABLE t1;
 End of 5.1 tests

mysql-test/t/alter_table.test

@@ -947,4 +947,16 @@ ALTER TABLE t1 CHANGE d c varchar(10);
 --disable_info
 DROP TABLE t1;
 
+
+#
+# Bug #23113: Different behavior on altering ENUM fields between 5.0 and 5.1
+#
+CREATE TABLE t1(a INT AUTO_INCREMENT PRIMARY KEY, 
+  b ENUM('a', 'b', 'c') NOT NULL);
+INSERT INTO t1 (b) VALUES ('a'), ('c'), ('b'), ('b'), ('a');
+ALTER TABLE t1 MODIFY b ENUM('a', 'z', 'b', 'c') NOT NULL;
+SELECT * FROM t1;
+DROP TABLE t1;
+
+
 --echo End of 5.1 tests

sql/field.cc

@@ -8783,28 +8783,43 @@ bool Field::eq_def(Field *field)
   return 1;
 }
 
+
 /**
   @return
   returns 1 if the fields are equally defined
 */
+
 bool Field_enum::eq_def(Field *field)
 {
   if (!Field::eq_def(field))
     return 0;
-  TYPELIB *from_lib=((Field_enum*) field)->typelib;
+  return compare_enum_values(((Field_enum*) field)->typelib);
+}
 
-  if (typelib->count < from_lib->count)
-    return 0;
-  for (uint i=0 ; i < from_lib->count ; i++)
+
+bool Field_enum::compare_enum_values(TYPELIB *values)
+{
+  if (typelib->count != values->count)
+    return FALSE;
+  for (uint i= 0; i < typelib->count; i++)
     if (my_strnncoll(field_charset,
-                     (const uchar*)typelib->type_names[i],
-                     strlen(typelib->type_names[i]),
-                     (const uchar*)from_lib->type_names[i],
-                     strlen(from_lib->type_names[i])))
+                     (const uchar*) typelib->type_names[i],
+                     typelib->type_lengths[i],
+                     (const uchar*) values->type_names[i],
+                     values->type_lengths[i]))
+      return FALSE;
+  return TRUE;
+}
+
+
+uint Field_enum::is_equal(Create_field *new_field)
+{
+  if (!Field_str::is_equal(new_field))
     return 0;
-  return 1;
+  return compare_enum_values(new_field->interval);
 }
 
+
 /**
   @return
   returns 1 if the fields are equally defined

sql/field.h

@@ -1853,6 +1853,8 @@ public:
   CHARSET_INFO *sort_charset(void) const { return &my_charset_bin; }
 private:
   int do_save_field_metadata(uchar *first_byte);
+  bool compare_enum_values(TYPELIB *values);
+  uint is_equal(Create_field *new_field);
 };