Fix bug#7672 Unknown column error in order clause

When fixing Item_func_plus in ORDER BY clause field c is searched in all
opened tables, but because c is an alias it wasn't found there.

This patch adds a flag to select_lex which allows Item_field::fix_fields() 
to look up in select's item_list to find aliased fields.

mysql-test/r/select.result

@@ -2431,3 +2431,13 @@ AND FK_firma_id = 2;
 COUNT(*)
 0
 drop table t1;
+CREATE TABLE t1 (a INT, b INT);
+(SELECT a, b AS c FROM t1) ORDER BY c+1;
+a	c
+(SELECT a, b AS c FROM t1) ORDER BY b+1;
+a	c
+SELECT a, b AS c FROM t1 ORDER BY c+1;
+a	c
+SELECT a, b AS c FROM t1 ORDER BY b+1;
+a	c
+drop table t1;

mysql-test/t/select.test

@@ -1983,3 +1983,12 @@ AND FK_firma_id = 2;
 
 drop table t1;
 
+#
+# Bug 7672 Unknown column error in order clause
+#
+CREATE TABLE t1 (a INT, b INT);
+(SELECT a, b AS c FROM t1) ORDER BY c+1;
+(SELECT a, b AS c FROM t1) ORDER BY b+1;
+SELECT a, b AS c FROM t1 ORDER BY c+1;
+SELECT a, b AS c FROM t1 ORDER BY b+1;
+drop table t1;

sql/item.cc

@@ -348,7 +348,18 @@ bool Item_field::fix_fields(THD *thd,TABLE_LIST *tables)
   {
     Field *tmp;
     if (!(tmp=find_field_in_tables(thd,this,tables)))
+    {
+      if (thd->lex.select_lex.is_item_list_lookup)
+      {
+        Item** res= find_item_in_list(this, thd->lex.select_lex.item_list);
+        if (res && *res && (*res)->type() == Item::FIELD_ITEM)
+        {
+          set_field((*((Item_field**)res))->field);
+          return 0;
+        }
+      }
       return 1;
+    }
     set_field(tmp);
   }
   else if (thd && thd->set_query_id && field->query_id != thd->query_id)

sql/sql_lex.cc

@@ -154,6 +154,7 @@ LEX *lex_start(THD *thd, uchar *buf,uint length)
   lex->slave_thd_opt=0;
   lex->sql_command=SQLCOM_END;
   bzero((char *)&lex->mi,sizeof(lex->mi));
+  lex->select_lex.is_item_list_lookup= 0;
   return lex;
 }
 

sql/sql_lex.h

@@ -121,7 +121,7 @@ typedef struct st_select_lex
 		      ignore_index, *ignore_index_ptr;
   List<Item_func_match> ftfunc_list;
   uint in_sum_expr, sort_default;
-  bool	create_refs, braces;
+  bool	create_refs, braces, is_item_list_lookup;
   st_select_lex *next;
 } SELECT_LEX;
 

sql/sql_select.cc

@@ -6845,8 +6845,14 @@ find_order_in_list(THD *thd,TABLE_LIST *tables,ORDER *order,List<Item> &fields,
     return 0;
   }
   order->in_field_list=0;
+  /* Allow lookup in select's item_list to find aliased fields */
+  thd->lex.select_lex.is_item_list_lookup= 1;
   if ((*order->item)->fix_fields(thd,tables) || thd->fatal_error)
+  {
+    thd->lex.select_lex.is_item_list_lookup= 0;
     return 1;					// Wrong field
+  }
+  thd->lex.select_lex.is_item_list_lookup= 0;
   all_fields.push_front(*order->item);		// Add new field to field list
   order->item=(Item**) all_fields.head_ref();
   return 0;