Fixed bug #27695.

Declaring an all space column name in the SELECT FROM DUAL or in a view
leads to misleading warning message:
"Leading spaces are removed from name ' '".

The Item::set_name method has been modified to raise warnings like
"Name ' ' has become ''" in case of the truncation of an all
space identifier to an empty string identifier instead of the
"Leading spaces are removed from name ' '" warning message.

mysql-test/r/select.result

@@ -4062,4 +4062,38 @@ SHOW WARNINGS;
 Level	Code	Message
 Note	1003	select '0' AS `c1` from `test`.`t1` `join_0` join `test`.`t1` `join_1` join `test`.`t1` `join_2` join `test`.`t1` `join_3` join `test`.`t1` `join_4` join `test`.`t1` `join_5` join `test`.`t1` `join_6` join `test`.`t1` `join_7` where 0 group by '0','0','0','0','0'
 DROP TABLE t1;
+SELECT 1 AS ` `;
+
+1
+Warnings:
+Warning	1474	Name ' ' has become ''
+SELECT 1 AS `  `;
+
+1
+Warnings:
+Warning	1474	Name '  ' has become ''
+SELECT 1 AS ` x`;
+x
+1
+Warnings:
+Warning	1466	Leading spaces are removed from name ' x'
+CREATE VIEW v1 AS SELECT 1 AS ` `;
+Warnings:
+Warning	1474	Name ' ' has become ''
+SELECT `` FROM v1;
+
+1
+CREATE VIEW v2 AS SELECT 1 AS `  `;
+Warnings:
+Warning	1474	Name '  ' has become ''
+SELECT `` FROM v2;
+
+1
+CREATE VIEW v3 AS SELECT 1 AS ` x`;
+Warnings:
+Warning	1466	Leading spaces are removed from name ' x'
+SELECT `x` FROM v3;
+x
+1
+DROP VIEW v1, v2, v3;
 End of 5.0 tests

mysql-test/t/select.test

@@ -3460,4 +3460,24 @@ SHOW WARNINGS;
 
 DROP TABLE t1;
 
+#
+# Bug #27695: Misleading warning when declaring all space column names and
+#             truncation of one-space column names to zero length names.
+#
+
+SELECT 1 AS ` `;
+SELECT 1 AS `  `;
+SELECT 1 AS ` x`;
+
+CREATE VIEW v1 AS SELECT 1 AS ` `;
+SELECT `` FROM v1;
+
+CREATE VIEW v2 AS SELECT 1 AS `  `;
+SELECT `` FROM v2;
+
+CREATE VIEW v3 AS SELECT 1 AS ` x`;
+SELECT `x` FROM v3;
+
+DROP VIEW v1, v2, v3;
+
 --echo End of 5.0 tests

sql/item.cc

@@ -700,10 +700,16 @@ void Item::set_name(const char *str, uint length, CHARSET_INFO *cs)
       str++;
     }
     if (orig_len != length && !is_autogenerated_name)
-      push_warning_printf(current_thd, MYSQL_ERROR::WARN_LEVEL_WARN,
-                          ER_REMOVED_SPACES, ER(ER_REMOVED_SPACES),
-                          str + length - orig_len);
-
+    {
+      if (length == 0)
+        push_warning_printf(current_thd, MYSQL_ERROR::WARN_LEVEL_WARN,
+                            ER_NAME_BECOMES_EMPTY, ER(ER_NAME_BECOMES_EMPTY),
+                            str + length - orig_len);
+      else
+        push_warning_printf(current_thd, MYSQL_ERROR::WARN_LEVEL_WARN,
+                            ER_REMOVED_SPACES, ER(ER_REMOVED_SPACES),
+                            str + length - orig_len);
+    }
   }
   if (!my_charset_same(cs, system_charset_info))
   {

sql/share/errmsg.txt

@@ -5637,3 +5637,5 @@ ER_ADMIN_WRONG_MRG_TABLE
 	eng "Table '%-.64s' is differently defined or of non-MyISAM type or doesn't exist"
 ER_TOO_HIGH_LEVEL_OF_NESTING_FOR_SELECT
 	eng "Too high level of nesting for select"
+ER_NAME_BECOMES_EMPTY
+        eng "Name '%-.64s' has become ''"