FIxed bug #14927.

A query with a group by and having clauses could return a wrong
result set if the having condition contained a constant conjunct 
evaluated to FALSE.
It happened because the pushdown condition for table with
grouping columns lost its constant conjuncts.
Pushdown conditions are always built by the function make_cond_for_table
that ignores constant conjuncts. This is apparently not correct when
constant false conjuncts are present.

mysql-test/r/having.result

@@ -141,3 +141,20 @@ SUM(a)
 6
 4
 DROP TABLE t1;
+CREATE TABLE t1 (a int);
+INSERT INTO t1 VALUES (1), (2), (1), (3), (2), (1);
+SELECT a FROM t1 GROUP BY a HAVING a > 1;
+a
+2
+3
+SELECT a FROM t1 GROUP BY a HAVING 1 != 1 AND a > 1;
+a
+SELECT 0 AS x, a FROM t1 GROUP BY x,a HAVING x=1 AND a > 1;
+x	a
+EXPLAIN SELECT a FROM t1 GROUP BY a HAVING 1 != 1 AND a > 1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible HAVING
+EXPLAIN SELECT 0 AS x, a FROM t1 GROUP BY x,a HAVING x=1 AND a > 1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible HAVING
+DROP table t1;

mysql-test/t/having.test

@@ -135,4 +135,20 @@ SELECT SUM(a) FROM t1 GROUP BY a HAVING SUM(a);
 
 DROP TABLE t1;
 
+#
+# Bug #14927: HAVING clause containing constant false conjunct
+#
+
+CREATE TABLE t1 (a int);
+INSERT INTO t1 VALUES (1), (2), (1), (3), (2), (1);
+
+SELECT a FROM t1 GROUP BY a HAVING a > 1;
+SELECT a FROM t1 GROUP BY a HAVING 1 != 1 AND a > 1;
+SELECT 0 AS x, a FROM t1 GROUP BY x,a HAVING x=1 AND a > 1;
+
+EXPLAIN SELECT a FROM t1 GROUP BY a HAVING 1 != 1 AND a > 1;
+EXPLAIN SELECT 0 AS x, a FROM t1 GROUP BY x,a HAVING x=1 AND a > 1;
+
+DROP table t1;  
+
 # End of 4.1 tests

sql/sql_lex.cc

@@ -1074,6 +1074,7 @@ void st_select_lex::init_query()
   item_list.empty();
   join= 0;
   where= 0;
+  having= 0;
   olap= UNSPECIFIED_OLAP_TYPE;
   having_fix_field= 0;
   resolve_mode= NOMATTER_MODE;
@@ -1081,6 +1082,7 @@ void st_select_lex::init_query()
   ref_pointer_array= 0;
   select_n_having_items= 0;
   prep_where= 0;
+  prep_having= 0;
   subquery_in_having= explicit_limit= 0;
   parsing_place= NO_MATTER;
   is_item_list_lookup= 0;

sql/sql_lex.h

@@ -421,6 +421,7 @@ public:
   char *db, *db1, *table1, *db2, *table2;      	/* For outer join using .. */
   Item *where, *having;                         /* WHERE & HAVING clauses */
   Item *prep_where; /* saved WHERE clause for prepared statement processing */
+  Item *prep_having;/* saved HAVING clause for prepared statement processing */
   enum olap_type olap;
   SQL_LIST	      table_list, group_list;   /* FROM & GROUP BY clauses */
   List<Item>          item_list; /* list of fields & expressions */

sql/sql_prepare.cc

@@ -1665,10 +1665,11 @@ int mysql_stmt_prepare(THD *thd, char *packet, uint packet_length,
     for (; sl; sl= sl->next_select_in_list())
     {
       /*
-        Save WHERE clause pointers, because they may be changed
+        Save WHERE, HAVING clause pointers, because they may be changed
         during query optimisation.
       */
       sl->prep_where= sl->where;
+      sl->prep_having= sl->having;
       /*
         Switch off a temporary flag that prevents evaluation of
         subqueries in statement prepare.
@@ -1694,13 +1695,18 @@ static void reset_stmt_for_execute(Prepared_statement *stmt)
     /* remove option which was put by mysql_explain_union() */
     sl->options&= ~SELECT_DESCRIBE;
     /*
-      Copy WHERE clause pointers to avoid damaging they by optimisation
+      Copy WHERE, HAVING clause pointers to avoid damaging they by optimisation
     */
     if (sl->prep_where)
     {
       sl->where= sl->prep_where->copy_andor_structure(thd);
       sl->where->cleanup();
     }
+    if (sl->prep_having)
+    {
+      sl->having= sl->prep_having->copy_andor_structure(thd);
+      sl->having->cleanup();
+    }
     DBUG_ASSERT(sl->join == 0);
     ORDER *order;
     /* Fix GROUP list */

sql/sql_select.cc

@@ -501,13 +501,19 @@ JOIN::optimize()
     DBUG_RETURN(1);
   }
 
-  if (cond_value == Item::COND_FALSE ||
+  {
+    Item::cond_result having_value;
+    having= optimize_cond(thd, having, &having_value);
+
+    if (cond_value == Item::COND_FALSE || having_value == Item::COND_FALSE || 
         (!unit->select_limit_cnt && !(select_options & OPTION_FOUND_ROWS)))
     {						/* Impossible cond */
-    zero_result_cause= "Impossible WHERE";
+      zero_result_cause= having_value == Item::COND_FALSE ?
+                           "Impossible HAVING" : "Impossible WHERE";
       error= 0;
       DBUG_RETURN(0);
     }
+  }
 
   /* Optimize count(*), min() and max() */
   if (tables_list && tmp_table_param.sum_func_count && ! group_list)
@@ -4611,10 +4617,8 @@ optimize_cond(THD *thd, COND *conds, Item::cond_result *cond_value)
     DBUG_EXECUTE("info", print_where(conds, "after remove"););
   }
   else
-  {
     *cond_value= Item::COND_TRUE;
-    select->prep_where= 0;
-  }
+
   DBUG_RETURN(conds);
 }