Fix for bug #54459: Assertion failed: param.sort_length,

file .\filesort.cc, line 149 (part II)

Problem: the server didn't disregard sort order 
for some zero length tuples.

Fix: skip sort order in such a case 
(zero length NOT NULL string functions).

mysql-test/r/select.result

@@ -4782,4 +4782,19 @@ a	b	c
 SELECT * FROM t1 WHERE 102 < c;
 a	b	c
 DROP TABLE t1;
+#
+# Bug #54459: Assertion failed: param.sort_length, 
+# file .\filesort.cc, line 149 (part II)
+#
+CREATE TABLE t1(a ENUM('') NOT NULL);
+INSERT INTO t1 VALUES (), (), ();
+EXPLAIN SELECT 1 FROM t1 ORDER BY a COLLATE latin1_german2_ci;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	3	
+SELECT 1 FROM t1 ORDER BY a COLLATE latin1_german2_ci;
+1
+1
+1
+1
+DROP TABLE t1;
 End of 5.1 tests

mysql-test/t/select.test

@@ -4077,4 +4077,19 @@ SELECT * FROM t1 WHERE 102 < c;
 DROP TABLE t1;
 
 
+--echo #
+--echo # Bug #54459: Assertion failed: param.sort_length, 
+--echo # file .\filesort.cc, line 149 (part II)
+--echo #
+CREATE TABLE t1(a ENUM('') NOT NULL);
+INSERT INTO t1 VALUES (), (), ();
+EXPLAIN SELECT 1 FROM t1 ORDER BY a COLLATE latin1_german2_ci;
+SELECT 1 FROM t1 ORDER BY a COLLATE latin1_german2_ci;
+DROP TABLE t1;
+
+create table t1(a enum('a'))engine=myisam charset=latin1;
+insert into t1 values (''),(''),(''),(NULL);
+select a, substr(a, 0, 0) from t1 order by substr(a, 0, 0);
+select a, a collate latin1_german2_ci from t1 order by a collate latin1_german2_ci;
+
 --echo End of 5.1 tests

sql/sql_select.cc

@@ -564,13 +564,21 @@ JOIN::prepare(Item ***rref_pointer_array,
     {
       Item *item= *ord->item;
       /*
-        Disregard sort order if there's only "{VAR}CHAR(0) NOT NULL" fields
-        there. Such fields don't contain any data to sort.
+        Disregard sort order if there's only 
+        zero length NOT NULL fields (e.g. {VAR}CHAR(0) NOT NULL") or
+        zero length NOT NULL string functions there.
+        Such tuples don't contain any data to sort.
       */
       if (!real_order &&
-          (item->type() != Item::FIELD_ITEM ||
+           /* Not a zero length NOT NULL field */
+          ((item->type() != Item::FIELD_ITEM ||
             ((Item_field *) item)->field->maybe_null() ||
-           ((Item_field *) item)->field->sort_length()))
+            ((Item_field *) item)->field->sort_length()) &&
+           /* AND not a zero length NOT NULL string function. */
+           (item->type() != Item::FUNC_ITEM ||
+            item->maybe_null ||
+            item->result_type() != STRING_RESULT ||
+            item->max_length)))
         real_order= TRUE;
 
       if (item->with_sum_func && item->type() != Item::SUM_FUNC_ITEM)