Fixed BUG#1874: Don't call fix_fields() indiscriminately, it resets null_value

for some items, which made aggregates like MIN(), MAX() and SUM() fail.

mysql-test/r/sp.result

@@ -6,9 +6,9 @@ id   char(16) not null,
 data int not null
 );
 create table t2 (
-s   char(16) not null,
-i   int not null,
-d   double not null
+s   char(16),
+i   int,
+d   double
 );
 create procedure foo42()
 insert into test.t1 values ("foo", 42);
@@ -777,6 +777,30 @@ a
 2
 drop table t3;
 drop procedure bug1862;
+create procedure bug1874()
+begin
+declare x int;
+declare y double;
+select max(data) into x from t1;
+insert into t2 values ("max", x, 0);
+select min(data) into x from t1;
+insert into t2 values ("min", x, 0);
+select sum(data) into x from t1;
+insert into t2 values ("sum", x, 0);
+select avg(data) into y from t1;
+insert into t2 values ("avg", 0, y);
+end;
+insert into t1 (data) values (3), (1), (5), (9), (4);
+call bug1874();
+select * from t2;
+s	i	d
+max	9	0
+min	1	0
+sum	22	0
+avg	0	4.4
+delete from t1;
+delete from t2;
+drop procedure bug1874;
 drop table if exists fac;
 create table fac (n int unsigned not null primary key, f bigint unsigned);
 create procedure ifac(n int unsigned)

mysql-test/t/sp.test

@@ -15,9 +15,9 @@ create table t1 (
         data int not null
 );
 create table t2 (
-	s   char(16) not null,
-        i   int not null,
-	d   double not null
+	s   char(16),
+        i   int,
+	d   double
 );
 
 
@@ -921,6 +921,31 @@ drop table t3|
 drop procedure bug1862|
 
 
+#
+# BUG#1874
+#
+create procedure bug1874()
+begin
+  declare x int;
+  declare y double;
+  select max(data) into x from t1;
+  insert into t2 values ("max", x, 0);
+  select min(data) into x from t1;
+  insert into t2 values ("min", x, 0);
+  select sum(data) into x from t1;
+  insert into t2 values ("sum", x, 0);
+  select avg(data) into y from t1;
+  insert into t2 values ("avg", 0, y);
+end|
+
+insert into t1 (data) values (3), (1), (5), (9), (4)|
+call bug1874()|
+select * from t2|
+delete from t1|
+delete from t2|
+drop procedure bug1874|
+
+
 #
 # Some "real" examples
 #

sql/sp_head.cc

@@ -54,26 +54,40 @@ sp_eval_func_item(THD *thd, Item *it, enum enum_field_types type)
   it= it->this_item();
   DBUG_PRINT("info", ("type: %d", type));
 
-  if (it->fix_fields(thd, 0, &it))
+  if (!it->fixed && it->fix_fields(thd, 0, &it))
   {
     DBUG_PRINT("info", ("fix_fields() failed"));
     DBUG_RETURN(it);		// Shouldn't happen?
   }
 
   /* QQ How do we do this? Is there some better way? */
-  if (type == MYSQL_TYPE_NULL || it->is_null())
+  if (type == MYSQL_TYPE_NULL)
     it= new Item_null();
   else
   {
     switch (sp_map_result_type(type)) {
     case INT_RESULT:
-      DBUG_PRINT("info", ("INT_RESULT: %d", it->val_int()));
+      {
+	longlong i= it->val_int();
+
+	DBUG_PRINT("info", ("INT_RESULT: %d", i));
+	if (it->null_value)
+	  it= new Item_null();
+	else
 	  it= new Item_int(it->val_int());
 	break;
+      }
     case REAL_RESULT:
-      DBUG_PRINT("info", ("REAL_RESULT: %g", it->val()));
+      {
+	double d= it->val();
+
+	DBUG_PRINT("info", ("REAL_RESULT: %g", d));
+	if (it->null_value)
+	  it= new Item_null();
+	else
 	  it= new Item_real(it->val());
 	break;
+      }
     default:
       {
 	char buffer[MAX_FIELD_WIDTH];
@@ -81,6 +95,9 @@ sp_eval_func_item(THD *thd, Item *it, enum enum_field_types type)
 	String *s= it->val_str(&tmp);
 
 	DBUG_PRINT("info",("default result: %*s",s->length(),s->c_ptr_quick()));
+	if (it->null_value)
+	  it= new Item_null();
+	else
 	  it= new Item_string(thd->strmake(s->c_ptr_quick(), s->length()),
 			      s->length(), it->collation.collation);
 	break;