From f78a60593a8fc2d2a99f1146ce3ec95d4208bd14 Mon Sep 17 00:00:00 2001
From: "sergefp@mysql.com" <>
Date: Sat, 11 Dec 2004 19:59:09 +0300
Subject: Fix for BUG#6976: In Item_ref::Item_ref set maybe_null (and other
 fields fix_fields sets) to be the same as in (*ref), because
 Item_ref::fix_fields() will not be called.  Previously maybe_null was 0
 always and this produced a bogus state where maybe_null==0 && is_null() ==
 true which broke evaluation for some upper-level Items, like AND and OR.

---
 mysql-test/r/group_by.result | 12 ++++++++++++
 mysql-test/t/group_by.test   |  9 +++++++++
 sql/item.cc                  |  1 +
 sql/item.h                   | 14 +++++++++++++-
 4 files changed, 35 insertions(+), 1 deletion(-)

diff --git a/mysql-test/r/group_by.result b/mysql-test/r/group_by.result
index dba95614052..f636692c0d9 100644
--- a/mysql-test/r/group_by.result
+++ b/mysql-test/r/group_by.result
@@ -626,3 +626,15 @@ explain SELECT i, COUNT(DISTINCT(i)) FROM t1 GROUP BY j ORDER BY NULL;
 table	type	possible_keys	key	key_len	ref	rows	Extra
 t1	ALL	NULL	NULL	NULL	NULL	6	Using filesort
 DROP TABLE t1;
+create table t1 (a int);
+insert into t1 values(null);
+select min(a) is null from t1;
+min(a) is null
+1
+select min(a) is null or null from t1;
+min(a) is null or null
+1
+select 1 and min(a) is null from t1;
+1 and min(a) is null
+1
+drop table t1;
diff --git a/mysql-test/t/group_by.test b/mysql-test/t/group_by.test
index 58bb4b3e268..5af78b924f8 100644
--- a/mysql-test/t/group_by.test
+++ b/mysql-test/t/group_by.test
@@ -447,3 +447,12 @@ INSERT INTO t1 VALUES (1,2),(2,3),(4,5),(3,5),(1,5),(23,5);
 SELECT i, COUNT(DISTINCT(i)) FROM t1 GROUP BY j ORDER BY NULL;
 explain SELECT i, COUNT(DISTINCT(i)) FROM t1 GROUP BY j ORDER BY NULL;
 DROP TABLE t1;
+
+#Test for BUG#6976: Aggregate functions have incorrect NULL-ness
+create table t1 (a int);
+insert into t1 values(null);
+select min(a) is null from t1;
+select min(a) is null or null from t1;
+select 1 and min(a) is null from t1;
+drop table t1;
+
diff --git a/sql/item.cc b/sql/item.cc
index 739b5385b55..8737cc06bbd 100644
--- a/sql/item.cc
+++ b/sql/item.cc
@@ -687,6 +687,7 @@ bool Item_null::send(THD *thd, String *packet)
 /*
   This is used for HAVING clause
   Find field in select list having the same name
+  This is not always called, see also Item_ref::Item_ref
  */
 
 bool Item_ref::fix_fields(THD *thd,TABLE_LIST *tables)
diff --git a/sql/item.h b/sql/item.h
index f6f9e1c0621..cc6a846d6c1 100644
--- a/sql/item.h
+++ b/sql/item.h
@@ -401,7 +401,19 @@ public:
   Item_ref(char *db_par,char *table_name_par,char *field_name_par)
     :Item_ident(db_par,table_name_par,field_name_par),ref(0) {}
   Item_ref(Item **item, char *table_name_par,char *field_name_par)
-    :Item_ident(NullS,table_name_par,field_name_par),ref(item) {}
+    :Item_ident(NullS,table_name_par,field_name_par),ref(item)
+  {
+    /*
+      This ctor is called from Item_XXX::split_sum_func, and fix_fields will
+      not be called for *this, so we must setup everything here. **ref is 
+      already fixed at this point.
+    */
+    max_length= (*ref)->max_length;
+    decimals=	(*ref)->decimals;
+    binary=	(*ref)->binary;
+    with_sum_func= (*ref)->with_sum_func;
+    maybe_null= (*ref)->maybe_null;
+  }
   enum Type type() const		{ return REF_ITEM; }
   bool eq(const Item *item, bool binary_cmp) const
   { return (*ref)->eq(item, binary_cmp); }
-- 
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