BUG#34945: "ref_or_null queries that are null_rejecting and have a null value crash mysql"

- Apply Eric Bergen's patch: in join_read_always_key(), move ha_index_init() call
  to before the late NULLs filtering code.
- Backport function comments from 6.0.

mysql-test/r/null_key.result

@@ -429,3 +429,21 @@ Handler_read_prev	0
 Handler_read_rnd	0
 Handler_read_rnd_next	5
 DROP TABLE t1,t2,t3,t4;
+CREATE TABLE t1 (
+a int(11) default NULL,
+b int(11) default NULL,
+KEY a (a,b)
+);
+INSERT INTO t1 VALUES (0,10),(0,11),(0,12);
+CREATE TABLE t2 (
+a int(11) default NULL,
+b int(11) default NULL,
+KEY a (a)
+);
+INSERT INTO t2 VALUES (3,NULL),(3,11),(3,12);
+SELECT * FROM t2 inner join t1 WHERE ( t1.a = 0 OR t1.a IS NULL) AND t2.a = 3 AND t2.b = t1.b;
+a	b	a	b
+3	11	0	11
+3	12	0	12
+drop table t1, t2;
+End of 5.0 tests

mysql-test/t/null_key.test

@@ -240,3 +240,26 @@ SHOW STATUS LIKE "handler_read%";
 
 DROP TABLE t1,t2,t3,t4;
 # End of 4.1 tests
+
+#
+# BUG#34945 "ref_or_null queries that are null_rejecting and have a null value crash mysql"
+# 
+CREATE TABLE t1 (
+  a int(11) default NULL,
+  b int(11) default NULL,
+  KEY a (a,b)
+);
+INSERT INTO t1 VALUES (0,10),(0,11),(0,12);
+
+CREATE TABLE t2 (
+  a int(11) default NULL,
+  b int(11) default NULL,
+  KEY a (a)
+);
+INSERT INTO t2 VALUES (3,NULL),(3,11),(3,12);
+
+SELECT * FROM t2 inner join t1 WHERE ( t1.a = 0 OR t1.a IS NULL) AND t2.a = 3 AND t2.b = t1.b;
+
+drop table t1, t2;
+-- echo End of 5.0 tests
+

sql/sql_select.cc

@@ -11173,19 +11173,42 @@ join_read_key(JOIN_TAB *tab)
 }
 
 
+/*
+  ref access method implementation: "read_first" function
+
+  SYNOPSIS
+    join_read_always_key()
+      tab  JOIN_TAB of the accessed table
+
+  DESCRIPTION
+    This is "read_fist" function for the "ref" access method.
+   
+    The functon must leave the index initialized when it returns.
+    ref_or_null access implementation depends on that.
+
+  RETURN
+    0  - Ok
+   -1  - Row not found 
+    1  - Error
+*/
+
 static int
 join_read_always_key(JOIN_TAB *tab)
 {
   int error;
   TABLE *table= tab->table;
 
+  /* Initialize the index first */
+  if (!table->file->inited)
+    table->file->ha_index_init(tab->ref.key);
+
+  /* Perform "Late NULLs Filtering" (see internals manual for explanations) */
   for (uint i= 0 ; i < tab->ref.key_parts ; i++)
   {
     if ((tab->ref.null_rejecting & 1 << i) && tab->ref.items[i]->is_null())
         return -1;
-  } 
-  if (!table->file->inited)
-    table->file->ha_index_init(tab->ref.key);
+  }
+
   if (cp_buffer_from_ref(tab->join->thd, &tab->ref))
     return -1;
   if ((error=table->file->index_read(table->record[0],