Fix for MIN/MAX with empty tables

MIN(key_column) could in some cases return NULL on a column with NULL and other values.
MIN(key_column) and MAX(key_column) could in some cases return wrong values when used in OUTER JOIN.

configure.in

@@ -4,7 +4,7 @@ dnl Process this file with autoconf to produce a configure script.
 AC_INIT(sql/mysqld.cc)
 AC_CANONICAL_SYSTEM
 # The Docs Makefile.am parses this line!
-AM_INIT_AUTOMAKE(mysql, 4.0.10-gamma)
+AM_INIT_AUTOMAKE(mysql, 4.0.11)
 AM_CONFIG_HEADER(config.h)
 
 PROTOCOL_VERSION=10

libmysqld/libmysqld.c

@@ -62,7 +62,7 @@ my_string	mysql_unix_port=0;
 #define closesocket(A) close(A)
 #endif
 
-static void mysql_once_init(void);
+void STDCALL mysql_once_init(void);
 static MYSQL_DATA *read_rows (MYSQL *mysql,MYSQL_FIELD *fields,
 			      uint field_count);
 static int read_one_row(MYSQL *mysql,uint fields,MYSQL_ROW row,

mysql-test/r/func_group.result

@@ -151,3 +151,56 @@ sum(num)
 45.63
 51.80
 drop table t1;
+create table t1 (a1 int, a2 char(3), key k1(a1), key k2(a2));
+insert into t1 values(10,'aaa'), (10,null), (10,'bbb'), (20,'zzz');
+create table t2(a1 char(3), a2 int, a3 real, key k1(a1), key k2(a2, a1));
+select * from t1;
+a1	a2
+10	aaa
+10	NULL
+10	bbb
+20	zzz
+select min(a2) from t1;
+min(a2)
+aaa
+select max(t1.a1), max(t2.a2) from t1, t2;
+max(t1.a1)	max(t2.a2)
+NULL	NULL
+select max(t1.a1) from t1, t2;
+max(t1.a1)
+NULL
+select max(t2.a2), max(t1.a1) from t1, t2;
+max(t2.a2)	max(t1.a1)
+NULL	NULL
+explain select min(a2) from t1;
+Comment
+Select tables optimized away
+explain select max(t1.a1), max(t2.a2) from t1, t2;
+Comment
+No matching min/max row
+insert into t2 values('AAA', 10, 0.5);
+select max(t1.a1), max(t2.a1) from t1, t2 where t2.a2=9;
+max(t1.a1)	max(t2.a1)
+NULL	NULL
+select max(t2.a1), max(t1.a1) from t1, t2 where t2.a2=9;
+max(t2.a1)	max(t1.a1)
+NULL	NULL
+select t1.a1, t1.a2, t2.a1, t2.a2 from t1 left outer join t2 on t1.a1=10;
+a1	a2	a1	a2
+10	aaa	AAA	10
+10	NULL	AAA	10
+10	bbb	AAA	10
+20	zzz	NULL	NULL
+select max(t1.a2) from t1 left outer join t2 on t1.a1=10;
+max(t1.a2)
+zzz
+select max(t1.a2) from t1 left outer join t2 on t1.a1=10 where t1.a1=20;
+max(t1.a2)
+zzz
+select max(t1.a2) from t1 left outer join t2 on t1.a1=10 where t1.a1=10;
+max(t1.a2)
+bbb
+select max(t2.a1) from t1 left outer join t2 on t1.a2=t2.a1 and 1=0 where t2.a1='AAA';
+max(t2.a1)
+NULL
+drop table t1,t2;

mysql-test/t/func_group.test

@@ -99,3 +99,30 @@ insert into t1 values (5.2,'nem'),(8.64,'monty'),(11.12,'sinisa');
 select sum(num) from t1;
 select sum(num) from t1 group by user;
 drop table t1;
+
+#
+# Test problem with MIN() optimization in case of null values
+#
+
+create table t1 (a1 int, a2 char(3), key k1(a1), key k2(a2));
+insert into t1 values(10,'aaa'), (10,null), (10,'bbb'), (20,'zzz');
+create table t2(a1 char(3), a2 int, a3 real, key k1(a1), key k2(a2, a1));
+select * from t1;
+# The following returned NULL in 4.0.10
+select min(a2) from t1;
+select max(t1.a1), max(t2.a2) from t1, t2;
+select max(t1.a1) from t1, t2;
+select max(t2.a2), max(t1.a1) from t1, t2;
+
+explain select min(a2) from t1;
+explain select max(t1.a1), max(t2.a2) from t1, t2;
+
+insert into t2 values('AAA', 10, 0.5);
+select max(t1.a1), max(t2.a1) from t1, t2 where t2.a2=9;
+select max(t2.a1), max(t1.a1) from t1, t2 where t2.a2=9;
+select t1.a1, t1.a2, t2.a1, t2.a2 from t1 left outer join t2 on t1.a1=10;
+select max(t1.a2) from t1 left outer join t2 on t1.a1=10;
+select max(t1.a2) from t1 left outer join t2 on t1.a1=10 where t1.a1=20;
+select max(t1.a2) from t1 left outer join t2 on t1.a1=10 where t1.a1=10;
+select max(t2.a1) from t1 left outer join t2 on t1.a2=t2.a1 and 1=0 where t2.a1='AAA';
+drop table t1,t2;

sql/item.h

@@ -89,6 +89,7 @@ public:
   virtual void set_result_field(Field *field) {}
   virtual bool is_result_field() { return 0; }
   virtual void save_in_result_field(bool no_conversions) {}
+  virtual void no_rows_in_result() {}
 };
 
 

sql/item_sum.h

@@ -69,6 +69,7 @@ public:
   void make_field(Send_field *field);
   void print(String *str);
   void fix_num_length_and_dec();
+  void no_rows_in_result() { reset(); }
   virtual bool setup(THD *thd) {return 0;}
   unsigned int size_of() { return sizeof(*this);}  
 };
@@ -135,6 +136,7 @@ class Item_sum_count :public Item_sum_int
   bool const_item() const { return !used_table_cache; }
   enum Sumfunctype sum_func () const { return COUNT_FUNC; }
   void reset();
+  void no_rows_in_result() { count=0; }
   bool add();
   void make_const(longlong count_arg) { count=count_arg; used_table_cache=0; }
   longlong val_int();

sql/opt_sum.cc

-/* Copyright (C) 2000 MySQL AB & MySQL Finland AB & TCX DataKonsult AB
+/* Copyright (C) 2000-2003 MySQL AB
 
    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
@@ -22,28 +22,55 @@
 
 static bool find_range_key(TABLE_REF *ref, Field* field,COND *cond);
 
-/*****************************************************************************
-** This function is only called for queries with sum functions and no
-** GROUP BY part.
-** This substitutes constants for some COUNT(), MIN() and MAX() functions.
-** The function returns 1 if all items was resolved and -1 on impossible
-** conditions
-****************************************************************************/
+/*
+  Substitutes constants for some COUNT(), MIN() and MAX() functions.
+
+  SYNOPSIS
+    opt_sum_query()
+    tables		Tables in query
+    all_fields		All fields to be returned
+    conds		WHERE clause
+
+  NOTE:
+    This function is only called for queries with sum functions and no
+    GROUP BY part.
+
+ RETURN VALUES
+    0 No errors
+    1 if all items was resolved
+   -1 on impossible  conditions
+*/
 
 int opt_sum_query(TABLE_LIST *tables, List<Item> &all_fields,COND *conds)
 {
   List_iterator_fast<Item> it(all_fields);
-  int const_result=1;
-  bool recalc_const_item=0;
-  table_map removed_tables=0;
+  int const_result= 1;
+  bool recalc_const_item= 0;
+  table_map removed_tables= 0, outer_tables= 0, used_tables= 0;
+  table_map where_tables= 0;
   Item *item;
   COND *org_conds= conds;
 
-  /* Add all ON conditions to WHERE condition */
+  if (conds)
+    where_tables= conds->used_tables();
+
+  /* Don't replace expression on a table that is part of an outer join */
   for (TABLE_LIST *tl=tables; tl ; tl= tl->next)
   {
     if (tl->on_expr)
-      conds= and_expressions(conds, tl->on_expr, &org_conds);
+    {
+      outer_tables|= tl->table->map;
+
+      /*
+	We can't optimise LEFT JOIN in cases where the WHERE condition
+	restricts the table that is used, like in:
+          SELECT MAX(t1.a) FROM t1 LEFT JOIN t2 join-condition
+	  WHERE t2.field IS NULL;
+      */
+      if (tl->table->map & where_tables)
+	return 0;
+    }
+    used_tables|= tl->table->map;
   }
 
   /*
@@ -68,8 +95,8 @@ int opt_sum_query(TABLE_LIST *tables, List<Item> &all_fields,COND *conds)
 	  TABLE_LIST *table;
 	  for (table=tables; table ; table=table->next)
 	  {
-	    if (table->on_expr || (table->table->file->table_flags() &
-				   HA_NOT_EXACT_COUNT))
+	    if (outer_tables || (table->table->file->table_flags() &
+				 HA_NOT_EXACT_COUNT))
 	    {
 	      const_result=0;			// Can't optimize left join
 	      break;
@@ -99,21 +126,35 @@ int opt_sum_query(TABLE_LIST *tables, List<Item> &all_fields,COND *conds)
 	  byte key_buff[MAX_KEY_LENGTH];
 	  TABLE_REF ref;
 	  ref.key_buff=key_buff;
+	  Item_field *item_field= ((Item_field*) expr);
+	  TABLE *table= item_field->field->table;
 
-	  if (!find_range_key(&ref, ((Item_field*) expr)->field,conds))
+	  if ((outer_tables & table->map) ||
+	      (!find_range_key(&ref, item_field->field,conds)))
 	  {
 	    const_result=0;
 	    break;
 	  }
-	  TABLE *table=((Item_field*) expr)->field->table;
-	  bool error=table->file->index_init((uint) ref.key);
+	  bool error= table->file->index_init((uint) ref.key);
+	  enum ha_rkey_function find_flag= HA_READ_KEY_OR_NEXT; 
+	  uint prefix_len= ref.key_length;
+	  /*
+	    If we are doing MIN() on a column with NULL fields
+	    we must read the key after the NULL column
+	  */
+	  if (item_field->field->null_bit)
+	  {
+	    ref.key_buff[ref.key_length++]=1;
+	    find_flag= HA_READ_AFTER_KEY;
+	  }
+
 	  if (!ref.key_length)
 	    error=table->file->index_first(table->record[0]) !=0;
 	  else
 	    error=table->file->index_read(table->record[0],key_buff,
 					  ref.key_length,
-					  HA_READ_KEY_OR_NEXT) ||
-	      key_cmp(table, key_buff, ref.key, ref.key_length);
+					  find_flag) ||
+	      key_cmp(table, key_buff, ref.key, prefix_len);
 	  if (table->key_read)
 	  {
 	    table->key_read=0;
@@ -121,7 +162,7 @@ int opt_sum_query(TABLE_LIST *tables, List<Item> &all_fields,COND *conds)
 	  }
 	  table->file->index_end();
 	  if (error)
-	    return -1;				// Impossible query
+	    return -1;				// No rows matching where
 	  removed_tables|= table->map;
 	}
 	else if (!expr->const_item())		// This is VERY seldom false
@@ -147,13 +188,14 @@ int opt_sum_query(TABLE_LIST *tables, List<Item> &all_fields,COND *conds)
 	  byte key_buff[MAX_KEY_LENGTH];
 	  TABLE_REF ref;
 	  ref.key_buff=key_buff;
+	  TABLE *table=((Item_field*) expr)->field->table;
 
-	  if (!find_range_key(&ref, ((Item_field*) expr)->field,conds))
+	  if ((outer_tables & table->map) ||
+	      !find_range_key(&ref, ((Item_field*) expr)->field,conds))
 	  {
 	    const_result=0;
 	    break;
 	  }
-	  TABLE *table=((Item_field*) expr)->field->table;
 	  if ((table->file->table_flags() & HA_NOT_READ_AFTER_KEY))
 	  {
 	    const_result=0;
@@ -203,8 +245,8 @@ int opt_sum_query(TABLE_LIST *tables, List<Item> &all_fields,COND *conds)
 	const_result=0;
     }
   }
-  if (conds && (conds->used_tables() & ~ removed_tables))
-    const_result=0;
+  if (used_tables != removed_tables)
+    const_result=0;				// We didn't remove all tables
   return const_result;
 }
 

sql/sql_select.cc

@@ -3104,7 +3104,13 @@ return_zero_rows(JOIN *join, select_result *result,TABLE_LIST *tables,
   if (!(result->send_fields(fields,1)))
   {
     if (send_row)
+    {
+      List_iterator_fast<Item> it(fields);
+      Item *item;
+      while ((item= it++))
+	item->no_rows_in_result();
       result->send_data(fields);
+    }
     if (tables)				// Not from do_select()
     {
       /* Close open cursors */