Bug #23280699: MYSQLD GOT SIGNAL 11 IN IS_NULL ON SELECT

               FROM I_S

Issue:
------
There is a difference in the field type created when the
following DDLs are used:

1) CREATE TABLE t0 AS SELECT NULL;
2) CREATE TABLE t0 AS SELECT GREATEST(NULL,NULL);

The first statement creates field of type Field_string and
the second one creates a field of type Field_null.

This creates a problem when the query mentioned in this bug
is used. Since the null_ptr is calculated differently for
Field_null.

Solution:
---------
When there is a function returning null in the select list
as mentioned above, the field should be of type
Field_string.

This was fixed in 5.6+ as part of Bug#14021323. This is a
backport to mysql-5.5.

An incorrect comment in innodb_bug54044.test has been
corrected in all versions.

1 files changed, 1 insertions, 4 deletions

diff --git a/sql/item.cc b/sql/item.cc
index 1541314ec97..34157c33cf4 100644
--- a/sql/item.cc
+++ b/sql/item.cc
@@ -5360,10 +5360,6 @@ Field *Item::tmp_table_field_from_field_type(TABLE *table, bool fixed_length)
     field= new Field_double((uchar*) 0, max_length, null_ptr, 0, Field::NONE,
 			    name, decimals, 0, unsigned_flag);
     break;
-  case MYSQL_TYPE_NULL:
-    field= new Field_null((uchar*) 0, max_length, Field::NONE,
-			  name, &my_charset_bin);
-    break;
   case MYSQL_TYPE_INT24:
     field= new Field_medium((uchar*) 0, max_length, null_ptr, 0, Field::NONE,
 			    name, 0, unsigned_flag);
@@ -5394,6 +5390,7 @@ Field *Item::tmp_table_field_from_field_type(TABLE *table, bool fixed_length)
     DBUG_ASSERT(0);
     /* If something goes awfully wrong, it's better to get a string than die */
   case MYSQL_TYPE_STRING:
+  case MYSQL_TYPE_NULL:
     if (fixed_length && max_length < CONVERT_IF_BIGGER_TO_BLOB)
     {
       field= new Field_string(max_length, maybe_null, name,